receive_imf.rs

//! Internet Message Format reception pipeline.

use std::collections::HashSet;
use std::iter;

use anyhow::{Context as _, Result};
use data_encoding::BASE32_NOPAD;
use deltachat_contact_tools::{addr_cmp, may_be_valid_addr, sanitize_single_line, ContactAddress};
use iroh_gossip::proto::TopicId;
use mailparse::SingleInfo;
use num_traits::FromPrimitive;
use once_cell::sync::Lazy;
use regex::Regex;

use crate::aheader::EncryptPreference;
use crate::chat::{self, Chat, ChatId, ChatIdBlocked, ProtectionStatus};
use crate::config::Config;
use crate::constants::{Blocked, Chattype, ShowEmails, DC_CHAT_ID_TRASH, EDITED_PREFIX};
use crate::contact::{Contact, ContactId, Origin};
use crate::context::Context;
use crate::debug_logging::maybe_set_logging_xdc_inner;
use crate::download::DownloadState;
use crate::ephemeral::{stock_ephemeral_timer_changed, Timer as EphemeralTimer};
use crate::events::EventType;
use crate::headerdef::{HeaderDef, HeaderDefMap};
use crate::imap::{markseen_on_imap_table, GENERATED_PREFIX};
use crate::log::LogExt;
use crate::message::{
    self, rfc724_mid_exists, Message, MessageState, MessengerMessage, MsgId, Viewtype,
};
use crate::mimeparser::{parse_message_ids, AvatarAction, MimeMessage, SystemMessage};
use crate::param::{Param, Params};
use crate::peer_channels::{add_gossip_peer_from_header, insert_topic_stub};
use crate::peerstate::Peerstate;
use crate::reaction::{set_msg_reaction, Reaction};
use crate::rusqlite::OptionalExtension;
use crate::securejoin::{self, handle_securejoin_handshake, observe_securejoin_on_other_device};
use crate::simplify;
use crate::stock_str;
use crate::sync::Sync::*;
use crate::tools::{self, buf_compress, remove_subject_prefix};
use crate::{chatlist_events, location};
use crate::{contact, imap};

/// This is the struct that is returned after receiving one email (aka MIME message).
///
/// One email with multiple attachments can end up as multiple chat messages, but they
/// all have the same chat_id, state and sort_timestamp.
#[derive(Debug)]
pub struct ReceivedMsg {
    /// Chat the message is assigned to.
    pub chat_id: ChatId,

    /// Received message state.
    pub state: MessageState,

    /// Whether the message is hidden.
    pub hidden: bool,

    /// Message timestamp for sorting.
    pub sort_timestamp: i64,

    /// IDs of inserted rows in messages table.
    pub msg_ids: Vec<MsgId>,

    /// Whether IMAP messages should be immediately deleted.
    pub needs_delete_job: bool,

    /// Whether the From address was repeated in the signed part
    /// (and we know that the signer intended to send from this address).
    #[cfg(test)]
    pub(crate) from_is_signed: bool,
}

/// Emulates reception of a message from the network.
///
/// This method returns errors on a failure to parse the mail or extract Message-ID. It's only used
/// for tests and REPL tool, not actual message reception pipeline.
#[cfg(any(test, feature = "internals"))]
pub async fn receive_imf(
    context: &Context,
    imf_raw: &[u8],
    seen: bool,
) -> Result<Option<ReceivedMsg>> {
    let mail = mailparse::parse_mail(imf_raw).context("can't parse mail")?;
    let rfc724_mid =
        imap::prefetch_get_message_id(&mail.headers).unwrap_or_else(imap::create_message_id);
    if let Some(download_limit) = context.download_limit().await? {
        let download_limit: usize = download_limit.try_into()?;
        if imf_raw.len() > download_limit {
            let head = std::str::from_utf8(imf_raw)?
                .split("\r\n\r\n")
                .next()
                .context("No empty line in the message")?;
            return receive_imf_from_inbox(
                context,
                &rfc724_mid,
                head.as_bytes(),
                seen,
                Some(imf_raw.len().try_into()?),
                false,
            )
            .await;
        }
    }
    receive_imf_from_inbox(context, &rfc724_mid, imf_raw, seen, None, false).await
}

/// Emulates reception of a message from "INBOX".
///
/// Only used for tests and REPL tool, not actual message reception pipeline.
#[cfg(any(test, feature = "internals"))]
pub(crate) async fn receive_imf_from_inbox(
    context: &Context,
    rfc724_mid: &str,
    imf_raw: &[u8],
    seen: bool,
    is_partial_download: Option<u32>,
    fetching_existing_messages: bool,
) -> Result<Option<ReceivedMsg>> {
    receive_imf_inner(
        context,
        "INBOX",
        0,
        0,
        rfc724_mid,
        imf_raw,
        seen,
        is_partial_download,
        fetching_existing_messages,
    )
    .await
}

/// Inserts a tombstone into `msgs` table
/// to prevent downloading the same message in the future.
///
/// Returns tombstone database row ID.
async fn insert_tombstone(context: &Context, rfc724_mid: &str) -> Result<MsgId> {
    let row_id = context
        .sql
        .insert(
            "INSERT INTO msgs(rfc724_mid, chat_id) VALUES (?,?)",
            (rfc724_mid, DC_CHAT_ID_TRASH),
        )
        .await?;
    let msg_id = MsgId::new(u32::try_from(row_id)?);
    Ok(msg_id)
}

/// Receive a message and add it to the database.
///
/// Returns an error on database failure or if the message is broken,
/// e.g. has nonstandard MIME structure.
///
/// If possible, creates a database entry to prevent the message from being
/// downloaded again, sets `chat_id=DC_CHAT_ID_TRASH` and returns `Ok(Some(…))`.
/// If the message is so wrong that we didn't even create a database entry,
/// returns `Ok(None)`.
///
/// If `is_partial_download` is set, it contains the full message size in bytes.
/// Do not confuse that with `replace_msg_id` that will be set when the full message is loaded
/// later.
#[expect(clippy::too_many_arguments)]
pub(crate) async fn receive_imf_inner(
    context: &Context,
    folder: &str,
    uidvalidity: u32,
    uid: u32,
    rfc724_mid: &str,
    imf_raw: &[u8],
    seen: bool,
    is_partial_download: Option<u32>,
    fetching_existing_messages: bool,
) -> Result<Option<ReceivedMsg>> {
    if std::env::var(crate::DCC_MIME_DEBUG).is_ok() {
        info!(
            context,
            "receive_imf: incoming message mime-body:\n{}",
            String::from_utf8_lossy(imf_raw),
        );
    }

    let mut mime_parser = match MimeMessage::from_bytes(context, imf_raw, is_partial_download).await
    {
        Err(err) => {
            warn!(context, "receive_imf: can't parse MIME: {err:#}.");
            if rfc724_mid.starts_with(GENERATED_PREFIX) {
                // We don't have an rfc724_mid, there's no point in adding a trash entry
                return Ok(None);
            }

            let msg_ids = vec![insert_tombstone(context, rfc724_mid).await?];

            return Ok(Some(ReceivedMsg {
                chat_id: DC_CHAT_ID_TRASH,
                state: MessageState::Undefined,
                hidden: false,
                sort_timestamp: 0,
                msg_ids,
                needs_delete_job: false,
                #[cfg(test)]
                from_is_signed: false,
            }));
        }
        Ok(mime_parser) => mime_parser,
    };

    crate::peerstate::maybe_do_aeap_transition(context, &mut mime_parser).await?;
    if let Some(peerstate) = &mime_parser.peerstate {
        peerstate
            .handle_fingerprint_change(context, mime_parser.timestamp_sent)
            .await?;
        // When peerstate is set to Mutual, it's saved immediately to not lose that fact in case
        // of an error. Otherwise we don't save peerstate until get here to reduce the number of
        // calls to save_to_db() and not to degrade encryption if a mail wasn't parsed
        // successfully.
        if peerstate.prefer_encrypt != EncryptPreference::Mutual {
            peerstate.save_to_db(&context.sql).await?;
        }
    }

    let rfc724_mid_orig = &mime_parser
        .get_rfc724_mid()
        .unwrap_or(rfc724_mid.to_string());
    info!(
        context,
        "Receiving message {rfc724_mid_orig:?}, seen={seen}...",
    );

    // check, if the mail is already in our database.
    // make sure, this check is done eg. before securejoin-processing.
    let (replace_msg_id, replace_chat_id);
    if let Some((old_msg_id, _)) = message::rfc724_mid_exists(context, rfc724_mid).await? {
        if is_partial_download.is_some() {
            // Should never happen, see imap::prefetch_should_download(), but still.
            info!(
                context,
                "Got a partial download and message is already in DB."
            );
            return Ok(None);
        }
        let msg = Message::load_from_db(context, old_msg_id).await?;
        replace_msg_id = Some(old_msg_id);
        replace_chat_id = if msg.download_state() != DownloadState::Done {
            // the message was partially downloaded before and is fully downloaded now.
            info!(
                context,
                "Message already partly in DB, replacing by full message."
            );
            Some(msg.chat_id)
        } else {
            None
        };
    } else {
        replace_msg_id = if rfc724_mid_orig == rfc724_mid {
            None
        } else if let Some((old_msg_id, old_ts_sent)) =
            message::rfc724_mid_exists(context, rfc724_mid_orig).await?
        {
            if imap::is_dup_msg(
                mime_parser.has_chat_version(),
                mime_parser.timestamp_sent,
                old_ts_sent,
            ) {
                info!(context, "Deleting duplicate message {rfc724_mid_orig}.");
                let target = context.get_delete_msgs_target().await?;
                context
                    .sql
                    .execute(
                        "UPDATE imap SET target=? WHERE folder=? AND uidvalidity=? AND uid=?",
                        (target, folder, uidvalidity, uid),
                    )
                    .await?;
            }
            Some(old_msg_id)
        } else {
            None
        };
        replace_chat_id = None;
    }

    if replace_chat_id.is_some() {
        // Need to update chat id in the db.
    } else if let Some(msg_id) = replace_msg_id {
        info!(context, "Message is already downloaded.");
        if mime_parser.incoming {
            return Ok(None);
        }
        // For the case if we missed a successful SMTP response. Be optimistic that the message is
        // delivered also.
        let self_addr = context.get_primary_self_addr().await?;
        context
            .sql
            .execute(
                "DELETE FROM smtp \
                WHERE rfc724_mid=?1 AND (recipients LIKE ?2 OR recipients LIKE ('% ' || ?2))",
                (rfc724_mid_orig, &self_addr),
            )
            .await?;
        if !context
            .sql
            .exists(
                "SELECT COUNT(*) FROM smtp WHERE rfc724_mid=?",
                (rfc724_mid_orig,),
            )
            .await?
        {
            msg_id.set_delivered(context).await?;
        }
        return Ok(None);
    };

    let prevent_rename =
        mime_parser.is_mailinglist_message() || mime_parser.get_header(HeaderDef::Sender).is_some();

    // get From: (it can be an address list!) and check if it is known (for known From:'s we add
    // the other To:/Cc: in the 3rd pass)
    // or if From: is equal to SELF (in this case, it is any outgoing messages,
    // we do not check Return-Path any more as this is unreliable, see
    // <https://github.com/deltachat/deltachat-core/issues/150>)
    //
    // If this is a mailing list email (i.e. list_id_header is some), don't change the displayname because in
    // a mailing list the sender displayname sometimes does not belong to the sender email address.
    // For example, GitHub sends messages from `notifications@github.com`,
    // but uses display name of the user whose action generated the notification
    // as the display name.
    let (from_id, _from_id_blocked, incoming_origin) =
        match from_field_to_contact_id(context, &mime_parser.from, prevent_rename).await? {
            Some(contact_id_res) => contact_id_res,
            None => {
                warn!(
                    context,
                    "receive_imf: From field does not contain an acceptable address."
                );
                return Ok(None);
            }
        };

    let to_ids = add_or_lookup_contacts_by_address_list(
        context,
        &mime_parser.recipients,
        if !mime_parser.incoming {
            Origin::OutgoingTo
        } else if incoming_origin.is_known() {
            Origin::IncomingTo
        } else {
            Origin::IncomingUnknownTo
        },
    )
    .await?;
    let past_ids = add_or_lookup_contacts_by_address_list(
        context,
        &mime_parser.past_members,
        if !mime_parser.incoming {
            Origin::OutgoingTo
        } else if incoming_origin.is_known() {
            Origin::IncomingTo
        } else {
            Origin::IncomingUnknownTo
        },
    )
    .await?;

    update_verified_keys(context, &mut mime_parser, from_id).await?;

    let received_msg;
    if mime_parser.get_header(HeaderDef::SecureJoin).is_some() {
        let res;
        if mime_parser.incoming {
            res = handle_securejoin_handshake(context, &mut mime_parser, from_id)
                .await
                .context("error in Secure-Join message handling")?;

            // Peerstate could be updated by handling the Securejoin handshake.
            let contact = Contact::get_by_id(context, from_id).await?;
            mime_parser.peerstate = Peerstate::from_addr(context, contact.get_addr()).await?;
        } else {
            let to_id = to_ids.first().copied().unwrap_or(ContactId::SELF);
            // handshake may mark contacts as verified and must be processed before chats are created
            res = observe_securejoin_on_other_device(context, &mime_parser, to_id)
                .await
                .context("error in Secure-Join watching")?
        }

        match res {
            securejoin::HandshakeMessage::Done | securejoin::HandshakeMessage::Ignore => {
                let msg_id = insert_tombstone(context, rfc724_mid).await?;
                received_msg = Some(ReceivedMsg {
                    chat_id: DC_CHAT_ID_TRASH,
                    state: MessageState::InSeen,
                    hidden: false,
                    sort_timestamp: mime_parser.timestamp_sent,
                    msg_ids: vec![msg_id],
                    needs_delete_job: res == securejoin::HandshakeMessage::Done,
                    #[cfg(test)]
                    from_is_signed: mime_parser.from_is_signed,
                });
            }
            securejoin::HandshakeMessage::Propagate => {
                received_msg = None;
            }
        }
    } else {
        received_msg = None;
    }

    let verified_encryption =
        has_verified_encryption(context, &mime_parser, from_id, &to_ids).await?;

    if verified_encryption == VerifiedEncryption::Verified
        && mime_parser.get_header(HeaderDef::ChatVerified).is_some()
    {
        if let Some(peerstate) = &mut mime_parser.peerstate {
            // NOTE: it might be better to remember ID of the key
            // that we used to decrypt the message, but
            // it is unlikely that default key ever changes
            // as it only happens when user imports a new default key.
            //
            // Backward verification is not security-critical,
            // it is only needed to avoid adding user who does not
            // have our key as verified to protected chats.
            peerstate.backward_verified_key_id =
                Some(context.get_config_i64(Config::KeyId).await?).filter(|&id| id > 0);
            peerstate.save_to_db(&context.sql).await?;
        }
    }

    let received_msg = if let Some(received_msg) = received_msg {
        received_msg
    } else {
        // Add parts
        add_parts(
            context,
            &mut mime_parser,
            imf_raw,
            &to_ids,
            &past_ids,
            rfc724_mid_orig,
            from_id,
            seen,
            is_partial_download,
            replace_msg_id,
            fetching_existing_messages,
            prevent_rename,
            verified_encryption,
        )
        .await
        .context("add_parts error")?
    };

    if !from_id.is_special() {
        contact::update_last_seen(context, from_id, mime_parser.timestamp_sent).await?;
    }

    // Update gossiped timestamp for the chat if someone else or our other device sent
    // Autocrypt-Gossip for all recipients in the chat to avoid sending Autocrypt-Gossip ourselves
    // and waste traffic.
    let chat_id = received_msg.chat_id;
    if !chat_id.is_special()
        && mime_parser.recipients.iter().all(|recipient| {
            recipient.addr == mime_parser.from.addr
                || mime_parser.gossiped_keys.contains_key(&recipient.addr)
        })
    {
        info!(
            context,
            "Received message contains Autocrypt-Gossip for all members of {chat_id}, updating timestamp."
        );
        if chat_id.get_gossiped_timestamp(context).await? < mime_parser.timestamp_sent {
            chat_id
                .set_gossiped_timestamp(context, mime_parser.timestamp_sent)
                .await?;
        }
    }

    let insert_msg_id = if let Some(msg_id) = received_msg.msg_ids.last() {
        *msg_id
    } else {
        MsgId::new_unset()
    };

    save_locations(context, &mime_parser, chat_id, from_id, insert_msg_id).await?;

    if let Some(ref sync_items) = mime_parser.sync_items {
        if from_id == ContactId::SELF {
            if mime_parser.was_encrypted() {
                context.execute_sync_items(sync_items).await;
            } else {
                warn!(context, "Sync items are not encrypted.");
            }
        } else {
            warn!(context, "Sync items not sent by self.");
        }
    }

    if let Some(ref status_update) = mime_parser.webxdc_status_update {
        let can_info_msg;
        let instance = if mime_parser
            .parts
            .first()
            .filter(|part| part.typ == Viewtype::Webxdc)
            .is_some()
        {
            can_info_msg = false;
            Some(Message::load_from_db(context, insert_msg_id).await?)
        } else if let Some(field) = mime_parser.get_header(HeaderDef::InReplyTo) {
            if let Some(instance) =
                message::get_by_rfc724_mids(context, &parse_message_ids(field)).await?
            {
                can_info_msg = instance.download_state() == DownloadState::Done;
                Some(instance)
            } else {
                can_info_msg = false;
                None
            }
        } else {
            can_info_msg = false;
            None
        };

        if let Some(instance) = instance {
            if let Err(err) = context
                .receive_status_update(
                    from_id,
                    &instance,
                    received_msg.sort_timestamp,
                    can_info_msg,
                    status_update,
                )
                .await
            {
                warn!(context, "receive_imf cannot update status: {err:#}.");
            }
        } else {
            warn!(
                context,
                "Received webxdc update, but cannot assign it to message."
            );
        }
    }

    if let Some(avatar_action) = &mime_parser.user_avatar {
        if from_id != ContactId::UNDEFINED
            && context
                .update_contacts_timestamp(
                    from_id,
                    Param::AvatarTimestamp,
                    mime_parser.timestamp_sent,
                )
                .await?
        {
            if let Err(err) = contact::set_profile_image(
                context,
                from_id,
                avatar_action,
                mime_parser.was_encrypted(),
            )
            .await
            {
                warn!(context, "receive_imf cannot update profile image: {err:#}.");
            };
        }
    }

    // Ignore footers from mailinglists as they are often created or modified by the mailinglist software.
    if let Some(footer) = &mime_parser.footer {
        if !mime_parser.is_mailinglist_message()
            && from_id != ContactId::UNDEFINED
            && context
                .update_contacts_timestamp(
                    from_id,
                    Param::StatusTimestamp,
                    mime_parser.timestamp_sent,
                )
                .await?
        {
            if let Err(err) = contact::set_status(
                context,
                from_id,
                footer.to_string(),
                mime_parser.was_encrypted(),
                mime_parser.has_chat_version(),
            )
            .await
            {
                warn!(context, "Cannot update contact status: {err:#}.");
            }
        }
    }

    // Get user-configured server deletion
    let delete_server_after = context.get_config_delete_server_after().await?;

    if !received_msg.msg_ids.is_empty() {
        let target = if received_msg.needs_delete_job
            || (delete_server_after == Some(0) && is_partial_download.is_none())
        {
            Some(context.get_delete_msgs_target().await?)
        } else {
            None
        };
        if target.is_some() || rfc724_mid_orig != rfc724_mid {
            let target_subst = match &target {
                Some(_) => "target=?1,",
                None => "",
            };
            context
                .sql
                .execute(
                    &format!("UPDATE imap SET {target_subst} rfc724_mid=?2 WHERE rfc724_mid=?3"),
                    (
                        target.as_deref().unwrap_or_default(),
                        rfc724_mid_orig,
                        rfc724_mid,
                    ),
                )
                .await?;
        }
        if target.is_none() && !mime_parser.mdn_reports.is_empty() && mime_parser.has_chat_version()
        {
            // This is a Delta Chat MDN. Mark as read.
            markseen_on_imap_table(context, rfc724_mid_orig).await?;
        }
    }

    if received_msg.hidden {
        // No need to emit an event about the changed message
    } else if let Some(replace_chat_id) = replace_chat_id {
        context.emit_msgs_changed_without_msg_id(replace_chat_id);
    } else if !chat_id.is_trash() {
        let fresh = received_msg.state == MessageState::InFresh;
        for msg_id in &received_msg.msg_ids {
            chat_id.emit_msg_event(context, *msg_id, mime_parser.incoming && fresh);
        }
    }
    context.new_msgs_notify.notify_one();

    mime_parser
        .handle_reports(context, from_id, &mime_parser.parts)
        .await;

    if let Some(is_bot) = mime_parser.is_bot {
        // If the message is auto-generated and was generated by Delta Chat,
        // mark the contact as a bot.
        if mime_parser.get_header(HeaderDef::ChatVersion).is_some() {
            from_id.mark_bot(context, is_bot).await?;
        }
    }

    Ok(Some(received_msg))
}

/// Converts "From" field to contact id.
///
/// Also returns whether it is blocked or not and its origin.
///
/// * `prevent_rename`: if true, the display_name of this contact will not be changed. Useful for
///   mailing lists: In some mailing lists, many users write from the same address but with different
///   display names. We don't want the display name to change every time the user gets a new email from
///   a mailing list.
///
/// Returns `None` if From field does not contain a valid contact address.
pub async fn from_field_to_contact_id(
    context: &Context,
    from: &SingleInfo,
    prevent_rename: bool,
) -> Result<Option<(ContactId, bool, Origin)>> {
    let display_name = if prevent_rename {
        Some("")
    } else {
        from.display_name.as_deref()
    };
    let from_addr = match ContactAddress::new(&from.addr) {
        Ok(from_addr) => from_addr,
        Err(err) => {
            warn!(
                context,
                "Cannot create a contact for the given From field: {err:#}."
            );
            return Ok(None);
        }
    };

    let (from_id, _) = Contact::add_or_lookup(
        context,
        display_name.unwrap_or_default(),
        &from_addr,
        Origin::IncomingUnknownFrom,
    )
    .await?;

    if from_id == ContactId::SELF {
        Ok(Some((ContactId::SELF, false, Origin::OutgoingBcc)))
    } else {
        let contact = Contact::get_by_id(context, from_id).await?;
        let from_id_blocked = contact.blocked;
        let incoming_origin = contact.origin;
        Ok(Some((from_id, from_id_blocked, incoming_origin)))
    }
}

/// Creates a `ReceivedMsg` from given parts which might consist of
/// multiple messages (if there are multiple attachments).
/// Every entry in `mime_parser.parts` produces a new row in the `msgs` table.
#[expect(clippy::too_many_arguments)]
async fn add_parts(
    context: &Context,
    mime_parser: &mut MimeMessage,
    imf_raw: &[u8],
    to_ids: &[ContactId],
    past_ids: &[ContactId],
    rfc724_mid: &str,
    from_id: ContactId,
    seen: bool,
    is_partial_download: Option<u32>,
    mut replace_msg_id: Option<MsgId>,
    fetching_existing_messages: bool,
    prevent_rename: bool,
    verified_encryption: VerifiedEncryption,
) -> Result<ReceivedMsg> {
    let is_bot = context.get_config_bool(Config::Bot).await?;
    // Bots handle existing messages the same way as new ones.
    let fetching_existing_messages = fetching_existing_messages && !is_bot;
    let rfc724_mid_orig = &mime_parser
        .get_rfc724_mid()
        .unwrap_or(rfc724_mid.to_string());

    let mut chat_id = None;
    let mut chat_id_blocked = Blocked::Not;

    let mut better_msg = None;
    let mut group_changes = GroupChangesInfo::default();
    if mime_parser.is_system_message == SystemMessage::LocationStreamingEnabled {
        better_msg = Some(stock_str::msg_location_enabled_by(context, from_id).await);
    }

    let parent = get_parent_message(
        context,
        mime_parser.get_header(HeaderDef::References),
        mime_parser.get_header(HeaderDef::InReplyTo),
    )
    .await?
    .filter(|p| Some(p.id) != replace_msg_id);

    let is_dc_message = if mime_parser.has_chat_version() {
        MessengerMessage::Yes
    } else if let Some(parent) = &parent {
        match parent.is_dc_message {
            MessengerMessage::No => MessengerMessage::No,
            MessengerMessage::Yes | MessengerMessage::Reply => MessengerMessage::Reply,
        }
    } else {
        MessengerMessage::No
    };
    // incoming non-chat messages may be discarded

    let is_location_kml = mime_parser.location_kml.is_some();
    let is_mdn = !mime_parser.mdn_reports.is_empty();
    let is_reaction = mime_parser.parts.iter().any(|part| part.is_reaction);
    let show_emails =
        ShowEmails::from_i32(context.get_config_int(Config::ShowEmails).await?).unwrap_or_default();

    let allow_creation;
    if mime_parser.is_system_message != SystemMessage::AutocryptSetupMessage
        && is_dc_message == MessengerMessage::No
    {
        // this message is a classic email not a chat-message nor a reply to one
        match show_emails {
            ShowEmails::Off => {
                info!(context, "Classical email not shown (TRASH).");
                chat_id = Some(DC_CHAT_ID_TRASH);
                allow_creation = false;
            }
            ShowEmails::AcceptedContacts => allow_creation = false,
            ShowEmails::All => allow_creation = !is_mdn,
        }
    } else {
        allow_creation = !is_mdn && !is_reaction;
    }

    // check if the message introduces a new chat:
    // - outgoing messages introduce a chat with the first to: address if they are sent by a messenger
    // - incoming messages introduce a chat only for known contacts if they are sent by a messenger
    // (of course, the user can add other chats manually later)
    let to_id: ContactId;
    let state: MessageState;
    let mut hidden = is_reaction;
    let mut needs_delete_job = false;
    let mut restore_protection = false;

    // if contact renaming is prevented (for mailinglists and bots),
    // we use name from From:-header as override name
    if prevent_rename {
        if let Some(name) = &mime_parser.from.display_name {
            for part in &mut mime_parser.parts {
                part.param.set(Param::OverrideSenderDisplayname, name);
            }
        }
    }

    if chat_id.is_none() && is_mdn {
        chat_id = Some(DC_CHAT_ID_TRASH);
        info!(context, "Message is an MDN (TRASH).",);
    }

    if mime_parser.incoming {
        to_id = ContactId::SELF;

        let test_normal_chat = ChatIdBlocked::lookup_by_contact(context, from_id).await?;

        if chat_id.is_none() && mime_parser.delivery_report.is_some() {
            chat_id = Some(DC_CHAT_ID_TRASH);
            info!(context, "Message is a DSN (TRASH).",);
            markseen_on_imap_table(context, rfc724_mid).await.ok();
        }

        let create_blocked_default = if is_bot {
            Blocked::Not
        } else {
            Blocked::Request
        };
        let create_blocked = if let Some(ChatIdBlocked { id: _, blocked }) = test_normal_chat {
            match blocked {
                Blocked::Request => create_blocked_default,
                Blocked::Not => Blocked::Not,
                Blocked::Yes => {
                    if Contact::is_blocked_load(context, from_id).await? {
                        // User has blocked the contact.
                        // Block the group contact created as well.
                        Blocked::Yes
                    } else {
                        // 1:1 chat is blocked, but the contact is not.
                        // This happens when 1:1 chat is hidden
                        // during scanning of a group invitation code.
                        create_blocked_default
                    }
                }
            }
        } else {
            create_blocked_default
        };

        // Try to assign to a chat based on Chat-Group-ID.
        if chat_id.is_none() {
            if let Some(grpid) = mime_parser.get_chat_group_id().map(|s| s.to_string()) {
                if let Some((id, _protected, blocked)) =
                    chat::get_chat_id_by_grpid(context, &grpid).await?
                {
                    chat_id = Some(id);
                    chat_id_blocked = blocked;
                } else if allow_creation || test_normal_chat.is_some() {
                    if let Some((new_chat_id, new_chat_id_blocked)) = create_group(
                        context,
                        mime_parser,
                        is_partial_download.is_some(),
                        create_blocked,
                        from_id,
                        to_ids,
                        past_ids,
                        &verified_encryption,
                        &grpid,
                    )
                    .await?
                    {
                        chat_id = Some(new_chat_id);
                        chat_id_blocked = new_chat_id_blocked;
                    }
                }
            }
        }

        if chat_id.is_none() {
            if let Some((new_chat_id, new_chat_id_blocked)) = lookup_chat_or_create_adhoc_group(
                context,
                mime_parser,
                &parent,
                to_ids,
                from_id,
                allow_creation || test_normal_chat.is_some(),
                create_blocked,
                is_partial_download.is_some(),
            )
            .await?
            {
                chat_id = Some(new_chat_id);
                chat_id_blocked = new_chat_id_blocked;
            }
        }

        // if the chat is somehow blocked but we want to create a non-blocked chat,
        // unblock the chat
        if chat_id_blocked != Blocked::Not && create_blocked != Blocked::Yes {
            if let Some(chat_id) = chat_id {
                chat_id.set_blocked(context, create_blocked).await?;
                chat_id_blocked = create_blocked;
            }
        }

        // In lookup_chat_by_reply() and create_group(), it can happen that the message is put into a chat
        // but the From-address is not a member of this chat.
        if let Some(group_chat_id) = chat_id {
            if !chat::is_contact_in_chat(context, group_chat_id, from_id).await? {
                let chat = Chat::load_from_db(context, group_chat_id).await?;
                if chat.is_protected() && chat.typ == Chattype::Single {
                    // Just assign the message to the 1:1 chat with the actual sender instead.
                    chat_id = None;
                } else {
                    // In non-protected chats, just mark the sender as overridden. Therefore, the UI will prepend `~`
                    // to the sender's name, indicating to the user that he/she is not part of the group.
                    let from = &mime_parser.from;
                    let name: &str = from.display_name.as_ref().unwrap_or(&from.addr);
                    for part in &mut mime_parser.parts {
                        part.param.set(Param::OverrideSenderDisplayname, name);

                        if chat.is_protected() {
                            // In protected chat, also mark the message with an error.
                            let s = stock_str::unknown_sender_for_chat(context).await;
                            part.error = Some(s);
                        }
                    }
                }
            }

            group_changes = apply_group_changes(
                context,
                mime_parser,
                group_chat_id,
                from_id,
                to_ids,
                past_ids,
                &verified_encryption,
            )
            .await?;
        }

        if chat_id.is_none() {
            // check if the message belongs to a mailing list
            if let Some(mailinglist_header) = mime_parser.get_mailinglist_header() {
                if let Some((new_chat_id, new_chat_id_blocked)) = create_or_lookup_mailinglist(
                    context,
                    allow_creation,
                    mailinglist_header,
                    mime_parser,
                )
                .await?
                {
                    chat_id = Some(new_chat_id);
                    chat_id_blocked = new_chat_id_blocked;
                }
            }
        }

        if let Some(chat_id) = chat_id {
            apply_mailinglist_changes(context, mime_parser, chat_id).await?;
        }

        if chat_id.is_none() {
            // try to create a normal chat
            let contact = Contact::get_by_id(context, from_id).await?;
            let create_blocked = match contact.is_blocked() {
                true => Blocked::Yes,
                false if is_bot => Blocked::Not,
                false => Blocked::Request,
            };

            if let Some(chat) = test_normal_chat {
                chat_id = Some(chat.id);
                chat_id_blocked = chat.blocked;
            } else if allow_creation {
                let chat = ChatIdBlocked::get_for_contact(context, from_id, create_blocked)
                    .await
                    .context("Failed to get (new) chat for contact")?;
                chat_id = Some(chat.id);
                chat_id_blocked = chat.blocked;
            }

            if let Some(chat_id) = chat_id {
                if chat_id_blocked != Blocked::Not {
                    if chat_id_blocked != create_blocked {
                        chat_id.set_blocked(context, create_blocked).await?;
                    }
                    if create_blocked == Blocked::Request && parent.is_some() {
                        // we do not want any chat to be created implicitly.  Because of the origin-scale-up,
                        // the contact requests will pop up and this should be just fine.
                        ContactId::scaleup_origin(context, &[from_id], Origin::IncomingReplyTo)
                            .await?;
                        info!(
                            context,
                            "Message is a reply to a known message, mark sender as known.",
                        );
                    }
                }

                // Check if the message was sent with verified encryption and set the protection of
                // the 1:1 chat accordingly.
                let chat = match is_partial_download.is_none()
                    && mime_parser.get_header(HeaderDef::SecureJoin).is_none()
                {
                    true => Some(Chat::load_from_db(context, chat_id).await?)
                        .filter(|chat| chat.typ == Chattype::Single),
                    false => None,
                };
                if let Some(chat) = chat {
                    debug_assert!(chat.typ == Chattype::Single);
                    let mut new_protection = match verified_encryption {
                        VerifiedEncryption::Verified => ProtectionStatus::Protected,
                        VerifiedEncryption::NotVerified(_) => ProtectionStatus::Unprotected,
                    };

                    if chat.protected != ProtectionStatus::Unprotected
                        && new_protection == ProtectionStatus::Unprotected
                        // `chat.protected` must be maintained regardless of the `Config::VerifiedOneOnOneChats`.
                        // That's why the config is checked here, and not above.
                        && context.get_config_bool(Config::VerifiedOneOnOneChats).await?
                    {
                        new_protection = ProtectionStatus::ProtectionBroken;
                    }
                    if chat.protected != new_protection {
                        // The message itself will be sorted under the device message since the device
                        // message is `MessageState::InNoticed`, which means that all following
                        // messages are sorted under it.
                        chat_id
                            .set_protection(
                                context,
                                new_protection,
                                mime_parser.timestamp_sent,
                                Some(from_id),
                            )
                            .await?;
                    }
                    if let Some(peerstate) = &mime_parser.peerstate {
                        restore_protection = new_protection != ProtectionStatus::Protected
                            && peerstate.prefer_encrypt == EncryptPreference::Mutual
                            // Check that the contact still has the Autocrypt key same as the
                            // verified key, see also `Peerstate::is_using_verified_key()`.
                            && contact.is_verified(context).await?;
                    }
                }
            }
        }

        state = if seen
            || fetching_existing_messages
            || is_mdn
            || chat_id_blocked == Blocked::Yes
            || group_changes.silent
        // No check for `hidden` because only reactions are such and they should be `InFresh`.
        {
            MessageState::InSeen
        } else {
            MessageState::InFresh
        };
    } else {
        // Outgoing

        // the mail is on the IMAP server, probably it is also delivered.
        // We cannot recreate other states (read, error).
        state = MessageState::OutDelivered;
        to_id = to_ids.first().copied().unwrap_or(ContactId::SELF);

        // Older Delta Chat versions with core <=1.152.2 only accepted
        // self-sent messages in Saved Messages with own address in the `To` field.
        // New Delta Chat versions may use empty `To` field
        // with only a single `hidden-recipients` group in this case.
        let self_sent = to_ids.len() <= 1 && to_id == ContactId::SELF;

        if mime_parser.sync_items.is_some() && self_sent {
            chat_id = Some(DC_CHAT_ID_TRASH);
        }

        // Mozilla Thunderbird does not set \Draft flag on "Templates", but sets
        // X-Mozilla-Draft-Info header, which can be used to detect both drafts and templates
        // created by Thunderbird.
        let is_draft = mime_parser
            .get_header(HeaderDef::XMozillaDraftInfo)
            .is_some();

        if is_draft {
            // Most mailboxes have a "Drafts" folder where constantly new emails appear but we don't actually want to show them
            info!(context, "Email is probably just a draft (TRASH).");
            chat_id = Some(DC_CHAT_ID_TRASH);
        }

        // Try to assign to a chat based on Chat-Group-ID.
        if chat_id.is_none() {
            if let Some(grpid) = mime_parser.get_chat_group_id().map(|s| s.to_string()) {
                if let Some((id, _protected, blocked)) =
                    chat::get_chat_id_by_grpid(context, &grpid).await?
                {
                    chat_id = Some(id);
                    chat_id_blocked = blocked;
                } else if allow_creation {
                    if let Some((new_chat_id, new_chat_id_blocked)) = create_group(
                        context,
                        mime_parser,
                        is_partial_download.is_some(),
                        Blocked::Not,
                        from_id,
                        to_ids,
                        past_ids,
                        &verified_encryption,
                        &grpid,
                    )
                    .await?
                    {
                        chat_id = Some(new_chat_id);
                        chat_id_blocked = new_chat_id_blocked;
                    }
                }
            }
        }

        if mime_parser.decrypting_failed && !fetching_existing_messages {
            if chat_id.is_none() {
                chat_id = Some(DC_CHAT_ID_TRASH);
            } else {
                hidden = true;
            }
            let last_time = context
                .get_config_i64(Config::LastCantDecryptOutgoingMsgs)
                .await?;
            let now = tools::time();
            let update_config = if last_time.saturating_add(24 * 60 * 60) <= now {
                let mut msg =
                    Message::new_text(stock_str::cant_decrypt_outgoing_msgs(context).await);
                chat::add_device_msg(context, None, Some(&mut msg))
                    .await
                    .log_err(context)
                    .ok();
                true
            } else {
                last_time > now
            };
            if update_config {
                context
                    .set_config_internal(
                        Config::LastCantDecryptOutgoingMsgs,
                        Some(&now.to_string()),
                    )
                    .await?;
            }
        }

        if chat_id.is_none() {
            if let Some((new_chat_id, new_chat_id_blocked)) = lookup_chat_or_create_adhoc_group(
                context,
                mime_parser,
                &parent,
                to_ids,
                from_id,
                allow_creation,
                Blocked::Not,
                is_partial_download.is_some(),
            )
            .await?
            {
                chat_id = Some(new_chat_id);
                chat_id_blocked = new_chat_id_blocked;
            }
        }

        if !to_ids.is_empty() {
            if chat_id.is_none() && allow_creation {
                let to_contact = Contact::get_by_id(context, to_id).await?;
                if let Some(list_id) = to_contact.param.get(Param::ListId) {
                    if let Some((id, _, blocked)) =
                        chat::get_chat_id_by_grpid(context, list_id).await?
                    {
                        chat_id = Some(id);
                        chat_id_blocked = blocked;
                    }
                } else {
                    let chat = ChatIdBlocked::get_for_contact(context, to_id, Blocked::Not).await?;
                    chat_id = Some(chat.id);
                    chat_id_blocked = chat.blocked;
                }
            }
            if chat_id.is_none() && is_dc_message == MessengerMessage::Yes {
                if let Some(chat) = ChatIdBlocked::lookup_by_contact(context, to_id).await? {
                    chat_id = Some(chat.id);
                    chat_id_blocked = chat.blocked;
                }
            }

            // automatically unblock chat when the user sends a message
            if chat_id_blocked != Blocked::Not {
                if let Some(chat_id) = chat_id {
                    chat_id.unblock_ex(context, Nosync).await?;
                    // Not assigning `chat_id_blocked = Blocked::Not` to avoid unused_assignments warning.
                }
            }
        }

        if let Some(chat_id) = chat_id {
            group_changes = apply_group_changes(
                context,
                mime_parser,
                chat_id,
                from_id,
                to_ids,
                past_ids,
                &verified_encryption,
            )
            .await?;
        }

        if chat_id.is_none() {
            // Check if the message belongs to a broadcast list.
            if let Some(mailinglist_header) = mime_parser.get_mailinglist_header() {
                let listid = mailinglist_header_listid(mailinglist_header)?;
                chat_id = Some(
                    if let Some((id, ..)) = chat::get_chat_id_by_grpid(context, &listid).await? {
                        id
                    } else {
                        let name =
                            compute_mailinglist_name(mailinglist_header, &listid, mime_parser);
                        chat::create_broadcast_list_ex(context, Nosync, listid, name).await?
                    },
                );
            }
        }

        if chat_id.is_none() && self_sent {
            // from_id==to_id==ContactId::SELF - this is a self-sent messages,
            // maybe an Autocrypt Setup Message
            let chat = ChatIdBlocked::get_for_contact(context, ContactId::SELF, Blocked::Not)
                .await
                .context("Failed to get (new) chat for contact")?;

            chat_id = Some(chat.id);
            // Not assigning `chat_id_blocked = chat.blocked` to avoid unused_assignments warning.

            if Blocked::Not != chat.blocked {
                chat.id.unblock_ex(context, Nosync).await?;
            }
        }
    }

    if fetching_existing_messages && mime_parser.decrypting_failed {
        chat_id = Some(DC_CHAT_ID_TRASH);
        // We are only gathering old messages on first start. We do not want to add loads of non-decryptable messages to the chats.
        info!(context, "Existing non-decipherable message (TRASH).");
    }

    if mime_parser.webxdc_status_update.is_some() && mime_parser.parts.len() == 1 {
        if let Some(part) = mime_parser.parts.first() {
            if part.typ == Viewtype::Text && part.msg.is_empty() {
                chat_id = Some(DC_CHAT_ID_TRASH);
                info!(context, "Message is a status update only (TRASH).");
                markseen_on_imap_table(context, rfc724_mid).await.ok();
            }
        }
    }

    let orig_chat_id = chat_id;
    let mut chat_id = chat_id.unwrap_or_else(|| {
        info!(context, "No chat id for message (TRASH).");
        DC_CHAT_ID_TRASH
    });

    // Extract ephemeral timer from the message or use the existing timer if the message is not fully downloaded.
    let mut ephemeral_timer = if is_partial_download.is_some() {
        chat_id.get_ephemeral_timer(context).await?
    } else if let Some(value) = mime_parser.get_header(HeaderDef::EphemeralTimer) {
        match value.parse::<EphemeralTimer>() {
            Ok(timer) => timer,
            Err(err) => {
                warn!(context, "Can't parse ephemeral timer \"{value}\": {err:#}.");
                EphemeralTimer::Disabled
            }
        }
    } else {
        EphemeralTimer::Disabled
    };

    let in_fresh = state == MessageState::InFresh;
    let sort_to_bottom = false;
    let received = true;
    let sort_timestamp = chat_id
        .calc_sort_timestamp(
            context,
            mime_parser.timestamp_sent,
            sort_to_bottom,
            received,
            mime_parser.incoming,
        )
        .await?;

    // Apply ephemeral timer changes to the chat.
    //
    // Only apply the timer when there are visible parts (e.g., the message does not consist only
    // of `location.kml` attachment).  Timer changes without visible received messages may be
    // confusing to the user.
    if !chat_id.is_special()
        && !mime_parser.parts.is_empty()
        && chat_id.get_ephemeral_timer(context).await? != ephemeral_timer
    {
        let chat_contacts =
            HashSet::<ContactId>::from_iter(chat::get_chat_contacts(context, chat_id).await?);
        let is_from_in_chat =
            !chat_contacts.contains(&ContactId::SELF) || chat_contacts.contains(&from_id);

        info!(context, "Received new ephemeral timer value {ephemeral_timer:?} for chat {chat_id}, checking if it should be applied.");
        if !is_from_in_chat {
            warn!(
                context,
                "Ignoring ephemeral timer change to {ephemeral_timer:?} for chat {chat_id} because sender {from_id} is not a member.",
            );
        } else if is_dc_message == MessengerMessage::Yes
            && get_previous_message(context, mime_parser)
                .await?
                .map(|p| p.ephemeral_timer)
                == Some(ephemeral_timer)
            && mime_parser.is_system_message != SystemMessage::EphemeralTimerChanged
        {
            // The message is a Delta Chat message, so we know that previous message according to
            // References header is the last message in the chat as seen by the sender. The timer
            // is the same in both the received message and the last message, so we know that the
            // sender has not seen any change of the timer between these messages. As our timer
            // value is different, it means the sender has not received some timer update that we
            // have seen or sent ourselves, so we ignore incoming timer to prevent a rollback.
            warn!(
                context,
                "Ignoring ephemeral timer change to {ephemeral_timer:?} for chat {chat_id} to avoid rollback.",
            );
        } else if chat_id
            .update_timestamp(
                context,
                Param::EphemeralSettingsTimestamp,
                mime_parser.timestamp_sent,
            )
            .await?
        {
            if let Err(err) = chat_id
                .inner_set_ephemeral_timer(context, ephemeral_timer)
                .await
            {
                warn!(
                    context,
                    "Failed to modify timer for chat {chat_id}: {err:#}."
                );
            } else {
                info!(
                    context,
                    "Updated ephemeral timer to {ephemeral_timer:?} for chat {chat_id}."
                );
                if mime_parser.is_system_message != SystemMessage::EphemeralTimerChanged {
                    chat::add_info_msg(
                        context,
                        chat_id,
                        &stock_ephemeral_timer_changed(context, ephemeral_timer, from_id).await,
                        sort_timestamp,
                    )
                    .await?;
                }
            }
        } else {
            warn!(
                context,
                "Ignoring ephemeral timer change to {ephemeral_timer:?} because it is outdated."
            );
        }
    }

    if mime_parser.is_system_message == SystemMessage::EphemeralTimerChanged {
        better_msg = Some(stock_ephemeral_timer_changed(context, ephemeral_timer, from_id).await);

        // Do not delete the system message itself.
        //
        // This prevents confusion when timer is changed
        // to 1 week, and then changed to 1 hour: after 1
        // hour, only the message about the change to 1
        // week is left.
        ephemeral_timer = EphemeralTimer::Disabled;
    }

    // if a chat is protected and the message is fully downloaded, check additional properties
    if !chat_id.is_special() && is_partial_download.is_none() {
        let chat = Chat::load_from_db(context, chat_id).await?;

        // For outgoing emails in the 1:1 chat we have an exception that
        // they are allowed to be unencrypted:
        // 1. They can't be an attack (they are outgoing, not incoming)
        // 2. Probably the unencryptedness is just a temporary state, after all
        //    the user obviously still uses DC
        //    -> Showing info messages every time would be a lot of noise
        // 3. The info messages that are shown to the user ("Your chat partner
        //    likely reinstalled DC" or similar) would be wrong.
        if chat.is_protected() && (mime_parser.incoming || chat.typ != Chattype::Single) {
            if let VerifiedEncryption::NotVerified(err) = verified_encryption {
                warn!(context, "Verification problem: {err:#}.");
                let s = format!("{err}. See 'Info' for more details");
                mime_parser.replace_msg_by_error(&s);
            }
        }
    }

    let sort_timestamp = tweak_sort_timestamp(
        context,
        mime_parser,
        group_changes.silent,
        chat_id,
        sort_timestamp,
    )
    .await?;

    let mime_in_reply_to = mime_parser
        .get_header(HeaderDef::InReplyTo)
        .unwrap_or_default();
    let mime_references = mime_parser
        .get_header(HeaderDef::References)
        .unwrap_or_default();

    // fine, so far.  now, split the message into simple parts usable as "short messages"
    // and add them to the database (mails sent by other messenger clients should result
    // into only one message; mails sent by other clients may result in several messages
    // (eg. one per attachment))
    let icnt = mime_parser.parts.len();

    let subject = mime_parser.get_subject().unwrap_or_default();

    let is_system_message = mime_parser.is_system_message;

    // if indicated by the parser,
    // we save the full mime-message and add a flag
    // that the ui should show button to display the full message.

    // We add "Show Full Message" button to the last message bubble (part) if this flag evaluates to
    // `true` finally.
    let mut save_mime_modified = false;

    let mime_headers = if mime_parser.is_mime_modified {
        let headers = if !mime_parser.decoded_data.is_empty() {
            mime_parser.decoded_data.clone()
        } else {
            imf_raw.to_vec()
        };
        tokio::task::block_in_place(move || buf_compress(&headers))?
    } else {
        Vec::new()
    };

    let mut created_db_entries = Vec::with_capacity(mime_parser.parts.len());

    if let Some(m) = group_changes.better_msg {
        match &better_msg {
            None => better_msg = Some(m),
            Some(_) => {
                if !m.is_empty() {
                    group_changes.extra_msgs.push((m, is_system_message))
                }
            }
        }
    }

    for (group_changes_msg, cmd) in group_changes.extra_msgs {
        chat::add_info_msg_with_cmd(
            context,
            chat_id,
            &group_changes_msg,
            cmd,
            sort_timestamp,
            None,
            None,
            None,
        )
        .await?;
    }

    if let Some(node_addr) = mime_parser.get_header(HeaderDef::IrohNodeAddr) {
        chat_id = DC_CHAT_ID_TRASH;
        match mime_parser.get_header(HeaderDef::InReplyTo) {
            Some(in_reply_to) => match rfc724_mid_exists(context, in_reply_to).await? {
                Some((instance_id, _ts_sent)) => {
                    if let Err(err) =
                        add_gossip_peer_from_header(context, instance_id, node_addr).await
                    {
                        warn!(context, "Failed to add iroh peer from header: {err:#}.");
                    }
                }
                None => {
                    warn!(
                        context,
                        "Cannot add iroh peer because WebXDC instance does not exist."
                    );
                }
            },
            None => {
                warn!(
                    context,
                    "Cannot add iroh peer because the message has no In-Reply-To."
                );
            }
        }
    }

    if let Some(rfc724_mid) = mime_parser.get_header(HeaderDef::ChatEdit) {
        chat_id = DC_CHAT_ID_TRASH;
        if let Some((original_msg_id, _)) = rfc724_mid_exists(context, rfc724_mid).await? {
            if let Some(mut original_msg) =
                Message::load_from_db_optional(context, original_msg_id).await?
            {
                if original_msg.from_id == from_id {
                    if let Some(part) = mime_parser.parts.first() {
                        let edit_msg_showpadlock = part
                            .param
                            .get_bool(Param::GuaranteeE2ee)
                            .unwrap_or_default();
                        if edit_msg_showpadlock || !original_msg.get_showpadlock() {
                            let new_text =
                                part.msg.strip_prefix(EDITED_PREFIX).unwrap_or(&part.msg);
                            chat::save_text_edit_to_db(context, &mut original_msg, new_text)
                                .await?;
                        } else {
                            warn!(context, "Edit message: Not encrypted.");
                        }
                    }
                } else {
                    warn!(context, "Edit message: Bad sender.");
                }
            } else {
                warn!(context, "Edit message: Database entry does not exist.");
            }
        } else {
            warn!(
                context,
                "Edit message: rfc724_mid {rfc724_mid:?} not found."
            );
        }
    } else if let Some(rfc724_mid_list) = mime_parser.get_header(HeaderDef::ChatDelete) {
        chat_id = DC_CHAT_ID_TRASH;
        if let Some(part) = mime_parser.parts.first() {
            // See `message::delete_msgs_ex()`, unlike edit requests, DC doesn't send unencrypted
            // deletion requests, so there's no need to support them.
            if part.param.get_bool(Param::GuaranteeE2ee).unwrap_or(false) {
                let mut modified_chat_ids = HashSet::new();
                let mut msg_ids = Vec::new();

                let rfc724_mid_vec: Vec<&str> = rfc724_mid_list.split_whitespace().collect();
                for rfc724_mid in rfc724_mid_vec {
                    if let Some((msg_id, _)) =
                        message::rfc724_mid_exists(context, rfc724_mid).await?
                    {
                        if let Some(msg) = Message::load_from_db_optional(context, msg_id).await? {
                            if msg.from_id == from_id {
                                message::delete_msg_locally(context, &msg).await?;
                                msg_ids.push(msg.id);
                                modified_chat_ids.insert(msg.chat_id);
                            } else {
                                warn!(context, "Delete message: Bad sender.");
                            }
                        } else {
                            warn!(context, "Delete message: Database entry does not exist.");
                        }
                    } else {
                        warn!(context, "Delete message: {rfc724_mid:?} not found.");
                    }
                }
                message::delete_msgs_locally_done(context, &msg_ids, modified_chat_ids).await?;
            } else {
                warn!(context, "Delete message: Not encrypted.");
            }
        }
    }

    let mut parts = mime_parser.parts.iter().peekable();
    while let Some(part) = parts.next() {
        if part.is_reaction {
            let reaction_str = simplify::remove_footers(part.msg.as_str());
            let is_incoming_fresh = mime_parser.incoming && !seen && !fetching_existing_messages;
            set_msg_reaction(
                context,
                mime_in_reply_to,
                orig_chat_id.unwrap_or_default(),
                from_id,
                sort_timestamp,
                Reaction::from(reaction_str.as_str()),
                is_incoming_fresh,
            )
            .await?;
        }

        let mut param = part.param.clone();
        if is_system_message != SystemMessage::Unknown {
            param.set_int(Param::Cmd, is_system_message as i32);
        }

        if let Some(replace_msg_id) = replace_msg_id {
            let placeholder = Message::load_from_db(context, replace_msg_id).await?;
            for key in [
                Param::WebxdcSummary,
                Param::WebxdcSummaryTimestamp,
                Param::WebxdcDocument,
                Param::WebxdcDocumentTimestamp,
            ] {
                if let Some(value) = placeholder.param.get(key) {
                    param.set(key, value);
                }
            }
        }

        let mut txt_raw = "".to_string();
        let (msg, typ): (&str, Viewtype) = if let Some(better_msg) = &better_msg {
            if better_msg.is_empty() && is_partial_download.is_none() {
                chat_id = DC_CHAT_ID_TRASH;
            }
            (better_msg, Viewtype::Text)
        } else {
            (&part.msg, part.typ)
        };
        let part_is_empty =
            typ == Viewtype::Text && msg.is_empty() && part.param.get(Param::Quote).is_none();

        save_mime_modified |= mime_parser.is_mime_modified && !part_is_empty && !hidden;
        let save_mime_modified = save_mime_modified && parts.peek().is_none();

        if part.typ == Viewtype::Text {
            let msg_raw = part.msg_raw.as_ref().cloned().unwrap_or_default();
            txt_raw = format!("{subject}\n\n{msg_raw}");
        }

        let ephemeral_timestamp = if in_fresh {
            0
        } else {
            match ephemeral_timer {
                EphemeralTimer::Disabled => 0,
                EphemeralTimer::Enabled { duration } => {
                    mime_parser.timestamp_rcvd.saturating_add(duration.into())
                }
            }
        };

        // If you change which information is skipped if the message is trashed,
        // also change `MsgId::trash()` and `delete_expired_messages()`
        let trash = chat_id.is_trash() || (is_location_kml && part_is_empty && !save_mime_modified);

        let row_id = context
            .sql
            .call_write(|conn| {
                let mut stmt = conn.prepare_cached(
            r#"
INSERT INTO msgs
  (
    id,
    rfc724_mid, chat_id,
    from_id, to_id, timestamp, timestamp_sent, 
    timestamp_rcvd, type, state, msgrmsg, 
    txt, txt_normalized, subject, txt_raw, param, hidden,
    bytes, mime_headers, mime_compressed, mime_in_reply_to,
    mime_references, mime_modified, error, ephemeral_timer,
    ephemeral_timestamp, download_state, hop_info
  )
  VALUES (
    ?,
    ?, ?, ?, ?,
    ?, ?, ?, ?,
    ?, ?, ?, ?, ?,
    ?, ?, ?, ?, ?, 1,
    ?, ?, ?, ?,
    ?, ?, ?, ?
  )
ON CONFLICT (id) DO UPDATE
SET rfc724_mid=excluded.rfc724_mid, chat_id=excluded.chat_id,
    from_id=excluded.from_id, to_id=excluded.to_id, timestamp_sent=excluded.timestamp_sent,
    type=excluded.type, state=max(state,excluded.state), msgrmsg=excluded.msgrmsg,
    txt=excluded.txt, txt_normalized=excluded.txt_normalized, subject=excluded.subject,
    txt_raw=excluded.txt_raw, param=excluded.param,
    hidden=excluded.hidden,bytes=excluded.bytes, mime_headers=excluded.mime_headers,
    mime_compressed=excluded.mime_compressed, mime_in_reply_to=excluded.mime_in_reply_to,
    mime_references=excluded.mime_references, mime_modified=excluded.mime_modified, error=excluded.error, ephemeral_timer=excluded.ephemeral_timer,
    ephemeral_timestamp=excluded.ephemeral_timestamp, download_state=excluded.download_state, hop_info=excluded.hop_info
RETURNING id
"#)?;
                let row_id: MsgId = stmt.query_row(params![
                    replace_msg_id,
                    rfc724_mid_orig,
                    if trash { DC_CHAT_ID_TRASH } else { chat_id },
                    if trash { ContactId::UNDEFINED } else { from_id },
                    if trash { ContactId::UNDEFINED } else { to_id },
                    sort_timestamp,
                    mime_parser.timestamp_sent,
                    mime_parser.timestamp_rcvd,
                    typ,
                    state,
                    is_dc_message,
                    if trash || hidden { "" } else { msg },
                    if trash || hidden { None } else { message::normalize_text(msg) },
                    if trash || hidden { "" } else { &subject },
                    // txt_raw might contain invalid utf8
                    if trash || hidden { "" } else { &txt_raw },
                    if trash {
                        "".to_string()
                    } else {
                        param.to_string()
                    },
                    hidden,
                    part.bytes as isize,
                    if save_mime_modified && !(trash || hidden) {
                        mime_headers.clone()
                    } else {
                        Vec::new()
                    },
                    mime_in_reply_to,
                    mime_references,
                    save_mime_modified,
                    part.error.as_deref().unwrap_or_default(),
                    ephemeral_timer,
                    ephemeral_timestamp,
                    if is_partial_download.is_some() {
                        DownloadState::Available
                    } else if mime_parser.decrypting_failed {
                        DownloadState::Undecipherable
                    } else {
                        DownloadState::Done
                    },
                    mime_parser.hop_info
                ],
                |row| {
                    let msg_id: MsgId = row.get(0)?;
                    Ok(msg_id)
                }
                )?;
                Ok(row_id)
            })
            .await?;

        // We only replace placeholder with a first part,
        // afterwards insert additional parts.
        replace_msg_id = None;

        debug_assert!(!row_id.is_special());
        created_db_entries.push(row_id);
    }

    // check all parts whether they contain a new logging webxdc
    for (part, msg_id) in mime_parser.parts.iter().zip(&created_db_entries) {
        // check if any part contains a webxdc topic id
        if part.typ == Viewtype::Webxdc {
            if let Some(topic) = mime_parser.get_header(HeaderDef::IrohGossipTopic) {
                // default encoding of topic ids is `hex`.
                let mut topic_raw = [0u8; 32];
                BASE32_NOPAD
                    .decode_mut(topic.to_ascii_uppercase().as_bytes(), &mut topic_raw)
                    .map_err(|e| e.error)
                    .context("Wrong gossip topic header")?;

                let topic = TopicId::from_bytes(topic_raw);
                insert_topic_stub(context, *msg_id, topic).await?;
            } else {
                warn!(context, "webxdc doesn't have a gossip topic")
            }
        }

        maybe_set_logging_xdc_inner(
            context,
            part.typ,
            chat_id,
            part.param.get(Param::Filename),
            *msg_id,
        )
        .await?;
    }

    if let Some(replace_msg_id) = replace_msg_id {
        // Trash the "replace" placeholder with a message that has no parts. If it has the original
        // "Message-ID", mark the placeholder for server-side deletion so as if the user deletes the
        // fully downloaded message later, the server-side deletion is issued.
        let on_server = rfc724_mid == rfc724_mid_orig;
        replace_msg_id.trash(context, on_server).await?;
    }

    let unarchive = match mime_parser.get_header(HeaderDef::ChatGroupMemberRemoved) {
        Some(addr) => context.is_self_addr(addr).await?,
        None => true,
    };
    if unarchive {
        chat_id.unarchive_if_not_muted(context, state).await?;
    }

    info!(
        context,
        "Message has {icnt} parts and is assigned to chat #{chat_id}."
    );

    if !chat_id.is_trash() && !hidden {
        let mut chat = Chat::load_from_db(context, chat_id).await?;

        // In contrast to most other update-timestamps,
        // use `sort_timestamp` instead of `sent_timestamp` for the subject-timestamp comparison.
        // This way, `LastSubject` actually refers to the most recent message _shown_ in the chat.
        if chat
            .param
            .update_timestamp(Param::SubjectTimestamp, sort_timestamp)?
        {
            // write the last subject even if empty -
            // otherwise a reply may get an outdated subject.
            let subject = mime_parser.get_subject().unwrap_or_default();

            chat.param.set(Param::LastSubject, subject);
            chat.update_param(context).await?;
        }
    }

    if !mime_parser.incoming && is_mdn && is_dc_message == MessengerMessage::Yes {
        // Normally outgoing MDNs sent by us never appear in mailboxes, but Gmail saves all
        // outgoing messages, including MDNs, to the Sent folder. If we detect such saved MDN,
        // delete it.
        needs_delete_job = true;
    }
    if restore_protection {
        chat_id
            .set_protection(
                context,
                ProtectionStatus::Protected,
                mime_parser.timestamp_rcvd,
                Some(from_id),
            )
            .await?;
    }
    Ok(ReceivedMsg {
        chat_id,
        state,
        hidden,
        sort_timestamp,
        msg_ids: created_db_entries,
        needs_delete_job,
        #[cfg(test)]
        from_is_signed: mime_parser.from_is_signed,
    })
}

async fn tweak_sort_timestamp(
    context: &Context,
    mime_parser: &mut MimeMessage,
    silent: bool,
    chat_id: ChatId,
    sort_timestamp: i64,
) -> Result<i64> {
    // Ensure replies to messages are sorted after the parent message.
    //
    // This is useful in a case where sender clocks are not
    // synchronized and parent message has a Date: header with a
    // timestamp higher than reply timestamp.
    //
    // This does not help if parent message arrives later than the
    // reply.
    let parent_timestamp = mime_parser.get_parent_timestamp(context).await?;
    let mut sort_timestamp = parent_timestamp.map_or(sort_timestamp, |parent_timestamp| {
        std::cmp::max(sort_timestamp, parent_timestamp)
    });

    // If the message should be silent,
    // set the timestamp to be no more than the same as last message
    // so that the chat is not sorted to the top of the chatlist.
    if silent {
        let last_msg_timestamp = if let Some(t) = chat_id.get_timestamp(context).await? {
            t
        } else {
            chat_id.created_timestamp(context).await?
        };
        sort_timestamp = std::cmp::min(sort_timestamp, last_msg_timestamp);
    }
    Ok(sort_timestamp)
}

/// Saves attached locations to the database.
///
/// Emits an event if at least one new location was added.
async fn save_locations(
    context: &Context,
    mime_parser: &MimeMessage,
    chat_id: ChatId,
    from_id: ContactId,
    msg_id: MsgId,
) -> Result<()> {
    if chat_id.is_special() {
        // Do not save locations for trashed messages.
        return Ok(());
    }

    let mut send_event = false;

    if let Some(message_kml) = &mime_parser.message_kml {
        if let Some(newest_location_id) =
            location::save(context, chat_id, from_id, &message_kml.locations, true).await?
        {
            location::set_msg_location_id(context, msg_id, newest_location_id).await?;
            send_event = true;
        }
    }

    if let Some(location_kml) = &mime_parser.location_kml {
        if let Some(addr) = &location_kml.addr {
            let contact = Contact::get_by_id(context, from_id).await?;
            if contact.get_addr().to_lowercase() == addr.to_lowercase() {
                if location::save(context, chat_id, from_id, &location_kml.locations, false)
                    .await?
                    .is_some()
                {
                    send_event = true;
                }
            } else {
                warn!(
                    context,
                    "Address in location.kml {:?} is not the same as the sender address {:?}.",
                    addr,
                    contact.get_addr()
                );
            }
        }
    }
    if send_event {
        context.emit_location_changed(Some(from_id)).await?;
    }
    Ok(())
}

async fn lookup_chat_by_reply(
    context: &Context,
    mime_parser: &MimeMessage,
    parent: &Option<Message>,
    to_ids: &[ContactId],
    from_id: ContactId,
) -> Result<Option<(ChatId, Blocked)>> {
    // Try to assign message to the same chat as the parent message.

    let Some(parent) = parent else {
        return Ok(None);
    };
    let Some(parent_chat_id) = ChatId::lookup_by_message(parent) else {
        return Ok(None);
    };
    let parent_chat = Chat::load_from_db(context, parent_chat_id).await?;

    // If this was a private message just to self, it was probably a private reply.
    // It should not go into the group then, but into the private chat.
    if is_probably_private_reply(context, to_ids, from_id, mime_parser, parent_chat.id).await? {
        return Ok(None);
    }

    // If the parent chat is a 1:1 chat, and the sender is a classical MUA and added
    // a new person to TO/CC, then the message should not go to the 1:1 chat, but to a
    // newly created ad-hoc group.
    if parent_chat.typ == Chattype::Single && !mime_parser.has_chat_version() && to_ids.len() > 1 {
        let mut chat_contacts = chat::get_chat_contacts(context, parent_chat.id).await?;
        chat_contacts.push(ContactId::SELF);
        if to_ids.iter().any(|id| !chat_contacts.contains(id)) {
            return Ok(None);
        }
    }

    info!(
        context,
        "Assigning message to {} as it's a reply to {}.", parent_chat.id, parent.rfc724_mid
    );
    Ok(Some((parent_chat.id, parent_chat.blocked)))
}

#[expect(clippy::too_many_arguments)]
async fn lookup_chat_or_create_adhoc_group(
    context: &Context,
    mime_parser: &MimeMessage,
    parent: &Option<Message>,
    to_ids: &[ContactId],
    from_id: ContactId,
    allow_creation: bool,
    create_blocked: Blocked,
    is_partial_download: bool,
) -> Result<Option<(ChatId, Blocked)>> {
    if let Some((new_chat_id, new_chat_id_blocked)) =
        // Try to assign to a chat based on In-Reply-To/References.
        lookup_chat_by_reply(context, mime_parser, parent, to_ids, from_id).await?
    {
        return Ok(Some((new_chat_id, new_chat_id_blocked)));
    }
    // Partial download may be an encrypted message with protected Subject header. We do not want to
    // create a group with "..." or "Encrypted message" as a subject. The same is for undecipherable
    // messages. Instead, assign the message to 1:1 chat with the sender.
    if is_partial_download {
        info!(
            context,
            "Ad-hoc group cannot be created from partial download."
        );
        return Ok(None);
    }
    if mime_parser.decrypting_failed {
        warn!(
            context,
            "Not creating ad-hoc group for message that cannot be decrypted."
        );
        return Ok(None);
    }

    let grpname = mime_parser
        .get_subject()
        .map(|s| remove_subject_prefix(&s))
        .unwrap_or_else(|| "👥📧".to_string());
    let mut contact_ids = Vec::with_capacity(to_ids.len() + 1);
    contact_ids.extend(to_ids);
    if !contact_ids.contains(&from_id) {
        contact_ids.push(from_id);
    }
    let trans_fn = |t: &mut rusqlite::Transaction| {
        t.pragma_update(None, "query_only", "0")?;
        t.execute(
            "CREATE TEMP TABLE temp.contacts (
                id INTEGER PRIMARY KEY
            ) STRICT",
            (),
        )?;
        let mut stmt = t.prepare("INSERT INTO temp.contacts(id) VALUES (?)")?;
        for &id in &contact_ids {
            stmt.execute((id,))?;
        }
        let val = t
            .query_row(
                "SELECT c.id, c.blocked
                FROM chats c INNER JOIN msgs m ON c.id=m.chat_id
                WHERE m.hidden=0 AND c.grpid='' AND c.name=?
                AND (SELECT COUNT(*) FROM chats_contacts
                     WHERE chat_id=c.id
                     AND add_timestamp >= remove_timestamp)=?
                AND (SELECT COUNT(*) FROM chats_contacts
                     WHERE chat_id=c.id
                     AND contact_id NOT IN (SELECT id FROM temp.contacts)
                     AND add_timestamp >= remove_timestamp)=0
                ORDER BY m.timestamp DESC",
                (&grpname, contact_ids.len()),
                |row| {
                    let id: ChatId = row.get(0)?;
                    let blocked: Blocked = row.get(1)?;
                    Ok((id, blocked))
                },
            )
            .optional()?;
        t.execute("DROP TABLE temp.contacts", ())?;
        Ok(val)
    };
    let query_only = true;
    if let Some((chat_id, blocked)) = context.sql.transaction_ex(query_only, trans_fn).await? {
        info!(
            context,
            "Assigning message to ad-hoc group {chat_id} with matching name and members."
        );
        return Ok(Some((chat_id, blocked)));
    }
    if !allow_creation {
        return Ok(None);
    }
    create_adhoc_group(
        context,
        mime_parser,
        create_blocked,
        from_id,
        to_ids,
        &grpname,
    )
    .await
    .context("Could not create ad hoc group")
}

/// If this method returns true, the message shall be assigned to the 1:1 chat with the sender.
/// If it returns false, it shall be assigned to the parent chat.
async fn is_probably_private_reply(
    context: &Context,
    to_ids: &[ContactId],
    from_id: ContactId,
    mime_parser: &MimeMessage,
    parent_chat_id: ChatId,
) -> Result<bool> {
    // Usually we don't want to show private replies in the parent chat, but in the
    // 1:1 chat with the sender.
    //
    // There is one exception: Classical MUA replies to two-member groups
    // should be assigned to the group chat. We restrict this exception to classical emails, as chat-group-messages
    // contain a Chat-Group-Id header and can be sorted into the correct chat this way.

    let private_message =
        (to_ids == [ContactId::SELF]) || (from_id == ContactId::SELF && to_ids.len() == 1);
    if !private_message {
        return Ok(false);
    }

    // Message cannot be a private reply if it has an explicit Chat-Group-ID header.
    if mime_parser.get_chat_group_id().is_some() {
        return Ok(false);
    }

    if !mime_parser.has_chat_version() {
        let chat_contacts = chat::get_chat_contacts(context, parent_chat_id).await?;
        if chat_contacts.len() == 2 && chat_contacts.contains(&ContactId::SELF) {
            return Ok(false);
        }
    }

    Ok(true)
}

/// This function tries to extract the group-id from the message and create a new group
/// chat with this ID. If there is no group-id and there are more
/// than two members, a new ad hoc group is created.
///
/// On success the function returns the created (chat_id, chat_blocked) tuple.
#[expect(clippy::too_many_arguments)]
async fn create_group(
    context: &Context,
    mime_parser: &mut MimeMessage,
    is_partial_download: bool,
    create_blocked: Blocked,
    from_id: ContactId,
    to_ids: &[ContactId],
    past_ids: &[ContactId],
    verified_encryption: &VerifiedEncryption,
    grpid: &str,
) -> Result<Option<(ChatId, Blocked)>> {
    let mut chat_id = None;
    let mut chat_id_blocked = Default::default();

    // For chat messages, we don't have to guess (is_*probably*_private_reply()) but we know for sure that
    // they belong to the group because of the Chat-Group-Id or Message-Id header
    if let Some(chat_id) = chat_id {
        if !mime_parser.has_chat_version()
            && is_probably_private_reply(context, to_ids, from_id, mime_parser, chat_id).await?
        {
            return Ok(None);
        }
    }

    let create_protected = if mime_parser.get_header(HeaderDef::ChatVerified).is_some() {
        if let VerifiedEncryption::NotVerified(err) = verified_encryption {
            warn!(context, "Verification problem: {err:#}.");
            let s = format!("{err}. See 'Info' for more details");
            mime_parser.replace_msg_by_error(&s);
        }
        ProtectionStatus::Protected
    } else {
        ProtectionStatus::Unprotected
    };

    async fn self_explicitly_added(
        context: &Context,
        mime_parser: &&mut MimeMessage,
    ) -> Result<bool> {
        let ret = match mime_parser.get_header(HeaderDef::ChatGroupMemberAdded) {
            Some(member_addr) => context.is_self_addr(member_addr).await?,
            None => false,
        };
        Ok(ret)
    }

    if chat_id.is_none()
            && !mime_parser.is_mailinglist_message()
            && !grpid.is_empty()
            && mime_parser.get_header(HeaderDef::ChatGroupName).is_some()
            // otherwise, a pending "quit" message may pop up
            && mime_parser.get_header(HeaderDef::ChatGroupMemberRemoved).is_none()
            // re-create explicitly left groups only if ourself is re-added
            && (!chat::is_group_explicitly_left(context, grpid).await?
                || self_explicitly_added(context, &mime_parser).await?)
    {
        // Group does not exist but should be created.
        let grpname = mime_parser
            .get_header(HeaderDef::ChatGroupName)
            .context("Chat-Group-Name vanished")?
            // Workaround for the "Space added before long group names after MIME
            // serialization/deserialization #3650" issue. DC itself never creates group names with
            // leading/trailing whitespace.
            .trim();
        let new_chat_id = ChatId::create_multiuser_record(
            context,
            Chattype::Group,
            grpid,
            grpname,
            create_blocked,
            create_protected,
            None,
            mime_parser.timestamp_sent,
        )
        .await
        .with_context(|| format!("Failed to create group '{grpname}' for grpid={grpid}"))?;

        chat_id = Some(new_chat_id);
        chat_id_blocked = create_blocked;

        // Create initial member list.
        if let Some(mut chat_group_member_timestamps) = mime_parser.chat_group_member_timestamps() {
            let mut new_to_ids = to_ids.to_vec();
            if !new_to_ids.contains(&from_id) {
                new_to_ids.insert(0, from_id);
                chat_group_member_timestamps.insert(0, mime_parser.timestamp_sent);
            }

            update_chats_contacts_timestamps(
                context,
                new_chat_id,
                None,
                &new_to_ids,
                past_ids,
                &chat_group_member_timestamps,
            )
            .await?;
        } else {
            let mut members = vec![ContactId::SELF];
            if !from_id.is_special() {
                members.push(from_id);
            }
            members.extend(to_ids);

            // Add all members with 0 timestamp
            // because we don't know the real timestamp of their addition.
            // This will allow other senders who support
            // `Chat-Group-Member-Timestamps` to overwrite
            // timestamps later.
            let timestamp = 0;

            chat::add_to_chat_contacts_table(context, timestamp, new_chat_id, &members).await?;
        }

        context.emit_event(EventType::ChatModified(new_chat_id));
        chatlist_events::emit_chatlist_changed(context);
        chatlist_events::emit_chatlist_item_changed(context, new_chat_id);
    }

    if let Some(chat_id) = chat_id {
        Ok(Some((chat_id, chat_id_blocked)))
    } else if is_partial_download || mime_parser.decrypting_failed {
        // It is possible that the message was sent to a valid,
        // yet unknown group, which was rejected because
        // Chat-Group-Name, which is in the encrypted part, was
        // not found. We can't create a properly named group in
        // this case, so assign error message to 1:1 chat with the
        // sender instead.
        Ok(None)
    } else {
        // The message was decrypted successfully, but contains a late "quit" or otherwise
        // unwanted message.
        info!(context, "Message belongs to unwanted group (TRASH).");
        Ok(Some((DC_CHAT_ID_TRASH, Blocked::Not)))
    }
}

async fn update_chats_contacts_timestamps(
    context: &Context,
    chat_id: ChatId,
    ignored_id: Option<ContactId>,
    to_ids: &[ContactId],
    past_ids: &[ContactId],
    chat_group_member_timestamps: &[i64],
) -> Result<bool> {
    let expected_timestamps_count = to_ids.len() + past_ids.len();

    if chat_group_member_timestamps.len() != expected_timestamps_count {
        warn!(
            context,
            "Chat-Group-Member-Timestamps has wrong number of timestamps, got {}, expected {}.",
            chat_group_member_timestamps.len(),
            expected_timestamps_count
        );
        return Ok(false);
    }

    let mut modified = false;

    context
        .sql
        .transaction(|transaction| {
            let mut add_statement = transaction.prepare(
                "INSERT INTO chats_contacts (chat_id, contact_id, add_timestamp)
                 VALUES                     (?1,      ?2,         ?3)
                 ON CONFLICT (chat_id, contact_id)
                 DO
                   UPDATE SET add_timestamp=?3
                   WHERE ?3>add_timestamp AND ?3>=remove_timestamp",
            )?;

            for (contact_id, ts) in iter::zip(
                to_ids.iter(),
                chat_group_member_timestamps.iter().take(to_ids.len()),
            ) {
                if Some(*contact_id) != ignored_id {
                    // It could be that member was already added,
                    // but updated addition timestamp
                    // is also a modification worth notifying about.
                    modified |= add_statement.execute((chat_id, contact_id, ts))? > 0;
                }
            }

            let mut remove_statement = transaction.prepare(
                "INSERT INTO chats_contacts (chat_id, contact_id, remove_timestamp)
                 VALUES                     (?1,      ?2,         ?3)
                 ON CONFLICT (chat_id, contact_id)
                 DO
                   UPDATE SET remove_timestamp=?3
                   WHERE ?3>remove_timestamp AND ?3>add_timestamp",
            )?;

            for (contact_id, ts) in iter::zip(
                past_ids.iter(),
                chat_group_member_timestamps.iter().skip(to_ids.len()),
            ) {
                // It could be that member was already removed,
                // but updated removal timestamp
                // is also a modification worth notifying about.
                modified |= remove_statement.execute((chat_id, contact_id, ts))? > 0;
            }

            Ok(())
        })
        .await?;

    Ok(modified)
}

/// The return type of [apply_group_changes].
/// Contains information on which system messages
/// should be shown in the chat.
#[derive(Default)]
struct GroupChangesInfo {
    /// Optional: A better message that should replace the original system message.
    /// If this is an empty string, the original system message should be trashed.
    better_msg: Option<String>,
    /// If true, the user should not be notified about the group change.
    silent: bool,
    /// A list of additional group changes messages that should be shown in the chat.
    extra_msgs: Vec<(String, SystemMessage)>,
}

/// Apply group member list, name, avatar and protection status changes from the MIME message.
///
/// Returns [GroupChangesInfo].
///
/// * `to_ids` - contents of the `To` and `Cc` headers.
/// * `past_ids` - contents of the `Chat-Group-Past-Members` header.
async fn apply_group_changes(
    context: &Context,
    mime_parser: &mut MimeMessage,
    chat_id: ChatId,
    from_id: ContactId,
    to_ids: &[ContactId],
    past_ids: &[ContactId],
    verified_encryption: &VerifiedEncryption,
) -> Result<GroupChangesInfo> {
    if chat_id.is_special() {
        // Do not apply group changes to the trash chat.
        return Ok(GroupChangesInfo::default());
    }
    let mut chat = Chat::load_from_db(context, chat_id).await?;
    if chat.typ != Chattype::Group {
        return Ok(GroupChangesInfo::default());
    }

    let mut send_event_chat_modified = false;
    let (mut removed_id, mut added_id) = (None, None);
    let mut better_msg = None;
    let mut silent = false;

    // True if a Delta Chat client has explicitly added our current primary address.
    let self_added =
        if let Some(added_addr) = mime_parser.get_header(HeaderDef::ChatGroupMemberAdded) {
            addr_cmp(&context.get_primary_self_addr().await?, added_addr)
        } else {
            false
        };

    let chat_contacts =
        HashSet::<ContactId>::from_iter(chat::get_chat_contacts(context, chat_id).await?);
    let is_from_in_chat =
        !chat_contacts.contains(&ContactId::SELF) || chat_contacts.contains(&from_id);

    if mime_parser.get_header(HeaderDef::ChatVerified).is_some() {
        if let VerifiedEncryption::NotVerified(err) = verified_encryption {
            warn!(context, "Verification problem: {err:#}.");
            let s = format!("{err}. See 'Info' for more details");
            mime_parser.replace_msg_by_error(&s);
        }

        if !chat.is_protected() {
            chat_id
                .set_protection(
                    context,
                    ProtectionStatus::Protected,
                    mime_parser.timestamp_sent,
                    Some(from_id),
                )
                .await?;
        }
    }

    if let Some(removed_addr) = mime_parser.get_header(HeaderDef::ChatGroupMemberRemoved) {
        removed_id = Contact::lookup_id_by_addr(context, removed_addr, Origin::Unknown).await?;
        if let Some(id) = removed_id {
            better_msg = if id == from_id {
                silent = true;
                Some(stock_str::msg_group_left_local(context, from_id).await)
            } else {
                Some(stock_str::msg_del_member_local(context, removed_addr, from_id).await)
            };
        } else {
            warn!(context, "Removed {removed_addr:?} has no contact id.")
        }
    } else if let Some(added_addr) = mime_parser.get_header(HeaderDef::ChatGroupMemberAdded) {
        if let Some(contact_id) =
            Contact::lookup_id_by_addr(context, added_addr, Origin::Unknown).await?
        {
            added_id = Some(contact_id);
        } else {
            warn!(context, "Added {added_addr:?} has no contact id.");
        }

        better_msg = Some(stock_str::msg_add_member_local(context, added_addr, from_id).await);
    }

    let group_name_timestamp = mime_parser
        .get_header(HeaderDef::ChatGroupNameTimestamp)
        .and_then(|s| s.parse::<i64>().ok());
    if let Some(old_name) = mime_parser
        .get_header(HeaderDef::ChatGroupNameChanged)
        .map(|s| s.trim())
        .or(match group_name_timestamp {
            Some(0) => None,
            Some(_) => Some(chat.name.as_str()),
            None => None,
        })
    {
        if let Some(grpname) = mime_parser
            .get_header(HeaderDef::ChatGroupName)
            .map(|grpname| grpname.trim())
            .filter(|grpname| grpname.len() < 200)
        {
            let grpname = &sanitize_single_line(grpname);
            let old_name = &sanitize_single_line(old_name);

            let chat_group_name_timestamp =
                chat.param.get_i64(Param::GroupNameTimestamp).unwrap_or(0);
            let group_name_timestamp = group_name_timestamp.unwrap_or(mime_parser.timestamp_sent);
            // To provide group name consistency, compare names if timestamps are equal.
            if (chat_group_name_timestamp, grpname) < (group_name_timestamp, old_name)
                && chat_id
                    .update_timestamp(context, Param::GroupNameTimestamp, group_name_timestamp)
                    .await?
            {
                info!(context, "Updating grpname for chat {chat_id}.");
                context
                    .sql
                    .execute("UPDATE chats SET name=? WHERE id=?;", (grpname, chat_id))
                    .await?;
                send_event_chat_modified = true;
            }
            if mime_parser
                .get_header(HeaderDef::ChatGroupNameChanged)
                .is_some()
            {
                better_msg.get_or_insert(
                    stock_str::msg_grp_name(context, old_name, grpname, from_id).await,
                );
            }
        }
    }

    if let (Some(value), None) = (mime_parser.get_header(HeaderDef::ChatContent), &better_msg) {
        if value == "group-avatar-changed" {
            if let Some(avatar_action) = &mime_parser.group_avatar {
                // this is just an explicit message containing the group-avatar,
                // apart from that, the group-avatar is send along with various other messages
                better_msg = match avatar_action {
                    AvatarAction::Delete => {
                        Some(stock_str::msg_grp_img_deleted(context, from_id).await)
                    }
                    AvatarAction::Change(_) => {
                        Some(stock_str::msg_grp_img_changed(context, from_id).await)
                    }
                };
            }
        }
    }

    if is_from_in_chat {
        if chat.member_list_is_stale(context).await? {
            info!(context, "Member list is stale.");
            let mut new_members: HashSet<ContactId> = HashSet::from_iter(to_ids.iter().copied());
            new_members.insert(ContactId::SELF);
            if !from_id.is_special() {
                new_members.insert(from_id);
            }

            context
                .sql
                .transaction(|transaction| {
                    // Remove all contacts and tombstones.
                    transaction.execute(
                        "DELETE FROM chats_contacts
                         WHERE chat_id=?",
                        (chat_id,),
                    )?;

                    // Insert contacts with default timestamps of 0.
                    let mut statement = transaction.prepare(
                        "INSERT INTO chats_contacts (chat_id, contact_id)
                         VALUES                     (?,       ?)",
                    )?;
                    for contact_id in &new_members {
                        statement.execute((chat_id, contact_id))?;
                    }

                    Ok(())
                })
                .await?;
            send_event_chat_modified = true;
        } else if let Some(ref chat_group_member_timestamps) =
            mime_parser.chat_group_member_timestamps()
        {
            send_event_chat_modified |= update_chats_contacts_timestamps(
                context,
                chat_id,
                Some(from_id),
                to_ids,
                past_ids,
                chat_group_member_timestamps,
            )
            .await?;
        } else {
            let mut new_members;
            if self_added {
                new_members = HashSet::from_iter(to_ids.iter().copied());
                new_members.insert(ContactId::SELF);
                if !from_id.is_special() {
                    new_members.insert(from_id);
                }
            } else {
                new_members = chat_contacts.clone();
            }

            // Allow non-Delta Chat MUAs to add members.
            if mime_parser.get_header(HeaderDef::ChatVersion).is_none() {
                // Don't delete any members locally, but instead add absent ones to provide group
                // membership consistency for all members:
                new_members.extend(to_ids.iter());
            }

            // Apply explicit addition if any.
            if let Some(added_id) = added_id {
                new_members.insert(added_id);
            }

            // Apply explicit removal if any.
            if let Some(removed_id) = removed_id {
                new_members.remove(&removed_id);
            }

            if new_members != chat_contacts {
                chat::update_chat_contacts_table(
                    context,
                    mime_parser.timestamp_sent,
                    chat_id,
                    &new_members,
                )
                .await?;
                send_event_chat_modified = true;
            }
        }

        chat_id
            .update_timestamp(
                context,
                Param::MemberListTimestamp,
                mime_parser.timestamp_sent,
            )
            .await?;
    }

    let new_chat_contacts = HashSet::<ContactId>::from_iter(
        chat::get_chat_contacts(context, chat_id)
            .await?
            .iter()
            .copied(),
    );

    // These are for adding info messages about implicit membership changes.
    let mut added_ids: HashSet<ContactId> = new_chat_contacts
        .difference(&chat_contacts)
        .copied()
        .collect();
    let mut removed_ids: HashSet<ContactId> = chat_contacts
        .difference(&new_chat_contacts)
        .copied()
        .collect();

    if let Some(added_id) = added_id {
        if !added_ids.remove(&added_id) && !self_added {
            // No-op "Member added" message.
            //
            // Trash it.
            better_msg = Some(String::new());
        }
    }
    if let Some(removed_id) = removed_id {
        removed_ids.remove(&removed_id);
    }
    let group_changes_msgs = if self_added {
        Vec::new()
    } else {
        group_changes_msgs(context, &added_ids, &removed_ids, chat_id).await?
    };

    if let Some(avatar_action) = &mime_parser.group_avatar {
        if !new_chat_contacts.contains(&ContactId::SELF) {
            warn!(
                context,
                "Received group avatar update for group chat {chat_id} we are not a member of."
            );
        } else if !new_chat_contacts.contains(&from_id) {
            warn!(
                context,
                "Contact {from_id} attempts to modify group chat {chat_id} avatar without being a member.",
            );
        } else {
            info!(context, "Group-avatar change for {chat_id}.");
            if chat
                .param
                .update_timestamp(Param::AvatarTimestamp, mime_parser.timestamp_sent)?
            {
                match avatar_action {
                    AvatarAction::Change(profile_image) => {
                        chat.param.set(Param::ProfileImage, profile_image);
                    }
                    AvatarAction::Delete => {
                        chat.param.remove(Param::ProfileImage);
                    }
                };
                chat.update_param(context).await?;
                send_event_chat_modified = true;
            }
        }
    }

    if send_event_chat_modified {
        context.emit_event(EventType::ChatModified(chat_id));
        chatlist_events::emit_chatlist_item_changed(context, chat_id);
    }
    Ok(GroupChangesInfo {
        better_msg,
        silent,
        extra_msgs: group_changes_msgs,
    })
}

/// Returns a list of strings that should be shown as info messages, informing about group membership changes.
async fn group_changes_msgs(
    context: &Context,
    added_ids: &HashSet<ContactId>,
    removed_ids: &HashSet<ContactId>,
    chat_id: ChatId,
) -> Result<Vec<(String, SystemMessage)>> {
    let mut group_changes_msgs = Vec::new();
    if !added_ids.is_empty() {
        warn!(
            context,
            "Implicit addition of {added_ids:?} to chat {chat_id}."
        );
    }
    if !removed_ids.is_empty() {
        warn!(
            context,
            "Implicit removal of {removed_ids:?} from chat {chat_id}."
        );
    }
    group_changes_msgs.reserve(added_ids.len() + removed_ids.len());
    for contact_id in added_ids {
        let contact = Contact::get_by_id(context, *contact_id).await?;
        group_changes_msgs.push((
            stock_str::msg_add_member_local(context, contact.get_addr(), ContactId::UNDEFINED)
                .await,
            SystemMessage::MemberAddedToGroup,
        ));
    }
    for contact_id in removed_ids {
        let contact = Contact::get_by_id(context, *contact_id).await?;
        group_changes_msgs.push((
            stock_str::msg_del_member_local(context, contact.get_addr(), ContactId::UNDEFINED)
                .await,
            SystemMessage::MemberRemovedFromGroup,
        ));
    }

    Ok(group_changes_msgs)
}

static LIST_ID_REGEX: Lazy<Regex> = Lazy::new(|| Regex::new(r"^(.+)<(.+)>$").unwrap());

fn mailinglist_header_listid(list_id_header: &str) -> Result<String> {
    Ok(match LIST_ID_REGEX.captures(list_id_header) {
        Some(cap) => cap.get(2).context("no match??")?.as_str().trim(),
        None => list_id_header
            .trim()
            .trim_start_matches('<')
            .trim_end_matches('>'),
    }
    .to_string())
}

/// Create or lookup a mailing list chat.
///
/// `list_id_header` contains the Id that must be used for the mailing list
/// and has the form `Name <Id>`, `<Id>` or just `Id`.
/// Depending on the mailing list type, `list_id_header`
/// was picked from `ListId:`-header or the `Sender:`-header.
///
/// `mime_parser` is the corresponding message
/// and is used to figure out the mailing list name from different header fields.
async fn create_or_lookup_mailinglist(
    context: &Context,
    allow_creation: bool,
    list_id_header: &str,
    mime_parser: &MimeMessage,
) -> Result<Option<(ChatId, Blocked)>> {
    let listid = mailinglist_header_listid(list_id_header)?;

    if let Some((chat_id, _, blocked)) = chat::get_chat_id_by_grpid(context, &listid).await? {
        return Ok(Some((chat_id, blocked)));
    }

    let name = compute_mailinglist_name(list_id_header, &listid, mime_parser);

    if allow_creation {
        // list does not exist but should be created
        let param = mime_parser.list_post.as_ref().map(|list_post| {
            let mut p = Params::new();
            p.set(Param::ListPost, list_post);
            p.to_string()
        });

        let is_bot = context.get_config_bool(Config::Bot).await?;
        let blocked = if is_bot {
            Blocked::Not
        } else {
            Blocked::Request
        };
        let chat_id = ChatId::create_multiuser_record(
            context,
            Chattype::Mailinglist,
            &listid,
            &name,
            blocked,
            ProtectionStatus::Unprotected,
            param,
            mime_parser.timestamp_sent,
        )
        .await
        .with_context(|| {
            format!(
                "failed to create mailinglist '{}' for grpid={}",
                &name, &listid
            )
        })?;

        chat::add_to_chat_contacts_table(
            context,
            mime_parser.timestamp_sent,
            chat_id,
            &[ContactId::SELF],
        )
        .await?;
        Ok(Some((chat_id, blocked)))
    } else {
        info!(context, "Creating list forbidden by caller.");
        Ok(None)
    }
}

fn compute_mailinglist_name(
    list_id_header: &str,
    listid: &str,
    mime_parser: &MimeMessage,
) -> String {
    let mut name = match LIST_ID_REGEX
        .captures(list_id_header)
        .and_then(|caps| caps.get(1))
    {
        Some(cap) => cap.as_str().trim().to_string(),
        None => "".to_string(),
    };

    // for mailchimp lists, the name in `ListId` is just a long number.
    // a usable name for these lists is in the `From` header
    // and we can detect these lists by a unique `ListId`-suffix.
    if listid.ends_with(".list-id.mcsv.net") {
        if let Some(display_name) = &mime_parser.from.display_name {
            name.clone_from(display_name);
        }
    }

    // additional names in square brackets in the subject are preferred
    // (as that part is much more visible, we assume, that names is shorter and comes more to the point,
    // than the sometimes longer part from ListId)
    let subject = mime_parser.get_subject().unwrap_or_default();
    static SUBJECT: Lazy<Regex> =
        Lazy::new(|| Regex::new(r"^.{0,5}\[(.+?)\](\s*\[.+\])?").unwrap()); // remove square brackets around first name
    if let Some(cap) = SUBJECT.captures(&subject) {
        name = cap[1].to_string() + cap.get(2).map_or("", |m| m.as_str());
    }

    // if we do not have a name yet and `From` indicates, that this is a notification list,
    // a usable name is often in the `From` header (seen for several parcel service notifications).
    // same, if we do not have a name yet and `List-Id` has a known suffix (`.xt.local`)
    //
    // this pattern is similar to mailchimp above, however,
    // with weaker conditions and does not overwrite existing names.
    if name.is_empty()
        && (mime_parser.from.addr.contains("noreply")
            || mime_parser.from.addr.contains("no-reply")
            || mime_parser.from.addr.starts_with("notifications@")
            || mime_parser.from.addr.starts_with("newsletter@")
            || listid.ends_with(".xt.local"))
    {
        if let Some(display_name) = &mime_parser.from.display_name {
            name.clone_from(display_name);
        }
    }

    // as a last resort, use the ListId as the name
    // but strip some known, long hash prefixes
    if name.is_empty() {
        // 51231231231231231231231232869f58.xing.com -> xing.com
        static PREFIX_32_CHARS_HEX: Lazy<Regex> =
            Lazy::new(|| Regex::new(r"([0-9a-fA-F]{32})\.(.{6,})").unwrap());
        if let Some(cap) = PREFIX_32_CHARS_HEX
            .captures(listid)
            .and_then(|caps| caps.get(2))
        {
            name = cap.as_str().to_string();
        } else {
            name = listid.to_string();
        }
    }

    sanitize_single_line(&name)
}

/// Set ListId param on the contact and ListPost param the chat.
/// Only called for incoming messages since outgoing messages never have a
/// List-Post header, anyway.
async fn apply_mailinglist_changes(
    context: &Context,
    mime_parser: &MimeMessage,
    chat_id: ChatId,
) -> Result<()> {
    let Some(mailinglist_header) = mime_parser.get_mailinglist_header() else {
        return Ok(());
    };

    let mut chat = Chat::load_from_db(context, chat_id).await?;
    if chat.typ != Chattype::Mailinglist {
        return Ok(());
    }
    let listid = &chat.grpid;

    let new_name = compute_mailinglist_name(mailinglist_header, listid, mime_parser);
    if chat.name != new_name
        && chat_id
            .update_timestamp(
                context,
                Param::GroupNameTimestamp,
                mime_parser.timestamp_sent,
            )
            .await?
    {
        info!(context, "Updating listname for chat {chat_id}.");
        context
            .sql
            .execute("UPDATE chats SET name=? WHERE id=?;", (new_name, chat_id))
            .await?;
        context.emit_event(EventType::ChatModified(chat_id));
    }

    let Some(list_post) = &mime_parser.list_post else {
        return Ok(());
    };

    let list_post = match ContactAddress::new(list_post) {
        Ok(list_post) => list_post,
        Err(err) => {
            warn!(context, "Invalid List-Post: {:#}.", err);
            return Ok(());
        }
    };
    let (contact_id, _) = Contact::add_or_lookup(context, "", &list_post, Origin::Hidden).await?;
    let mut contact = Contact::get_by_id(context, contact_id).await?;
    if contact.param.get(Param::ListId) != Some(listid) {
        contact.param.set(Param::ListId, listid);
        contact.update_param(context).await?;
    }

    if let Some(old_list_post) = chat.param.get(Param::ListPost) {
        if list_post.as_ref() != old_list_post {
            // Apparently the mailing list is using a different List-Post header in each message.
            // Make the mailing list read-only because we wouldn't know which message the user wants to reply to.
            chat.param.remove(Param::ListPost);
            chat.update_param(context).await?;
        }
    } else {
        chat.param.set(Param::ListPost, list_post);
        chat.update_param(context).await?;
    }

    Ok(())
}

/// Creates ad-hoc group and returns chat ID on success.
async fn create_adhoc_group(
    context: &Context,
    mime_parser: &MimeMessage,
    create_blocked: Blocked,
    from_id: ContactId,
    to_ids: &[ContactId],
    grpname: &str,
) -> Result<Option<(ChatId, Blocked)>> {
    let mut member_ids: Vec<ContactId> = to_ids.to_vec();
    if !member_ids.contains(&(from_id)) {
        member_ids.push(from_id);
    }
    if !member_ids.contains(&(ContactId::SELF)) {
        member_ids.push(ContactId::SELF);
    }

    if mime_parser.is_mailinglist_message() {
        return Ok(None);
    }
    if mime_parser
        .get_header(HeaderDef::ChatGroupMemberRemoved)
        .is_some()
    {
        info!(
            context,
            "Message removes member from unknown ad-hoc group (TRASH)."
        );
        return Ok(Some((DC_CHAT_ID_TRASH, Blocked::Not)));
    }
    if member_ids.len() < 3 {
        return Ok(None);
    }

    let new_chat_id: ChatId = ChatId::create_multiuser_record(
        context,
        Chattype::Group,
        "", // Ad hoc groups have no ID.
        grpname,
        create_blocked,
        ProtectionStatus::Unprotected,
        None,
        mime_parser.timestamp_sent,
    )
    .await?;

    info!(
        context,
        "Created ad-hoc group id={new_chat_id}, name={grpname:?}."
    );
    chat::add_to_chat_contacts_table(
        context,
        mime_parser.timestamp_sent,
        new_chat_id,
        &member_ids,
    )
    .await?;

    context.emit_event(EventType::ChatModified(new_chat_id));
    chatlist_events::emit_chatlist_changed(context);
    chatlist_events::emit_chatlist_item_changed(context, new_chat_id);

    Ok(Some((new_chat_id, create_blocked)))
}

#[derive(Debug, PartialEq, Eq)]
enum VerifiedEncryption {
    Verified,
    NotVerified(String), // The string contains the reason why it's not verified
}

/// Moves secondary verified key to primary verified key
/// if the message is signed with a secondary verified key.
/// Removes secondary verified key if the message is signed with primary key.
async fn update_verified_keys(
    context: &Context,
    mimeparser: &mut MimeMessage,
    from_id: ContactId,
) -> Result<Option<String>> {
    if from_id == ContactId::SELF {
        return Ok(None);
    }

    if !mimeparser.was_encrypted() {
        return Ok(None);
    }

    let Some(peerstate) = &mut mimeparser.peerstate else {
        // No peerstate means no verified keys.
        return Ok(None);
    };

    let signed_with_primary_verified_key = peerstate
        .verified_key_fingerprint
        .as_ref()
        .filter(|fp| mimeparser.signatures.contains(fp))
        .is_some();
    let signed_with_secondary_verified_key = peerstate
        .secondary_verified_key_fingerprint
        .as_ref()
        .filter(|fp| mimeparser.signatures.contains(fp))
        .is_some();

    if signed_with_primary_verified_key {
        // Remove secondary key if it exists.
        if peerstate.secondary_verified_key.is_some()
            || peerstate.secondary_verified_key_fingerprint.is_some()
            || peerstate.secondary_verifier.is_some()
        {
            peerstate.secondary_verified_key = None;
            peerstate.secondary_verified_key_fingerprint = None;
            peerstate.secondary_verifier = None;
            peerstate.save_to_db(&context.sql).await?;
        }

        // No need to notify about secondary key removal.
        Ok(None)
    } else if signed_with_secondary_verified_key {
        peerstate.verified_key = peerstate.secondary_verified_key.take();
        peerstate.verified_key_fingerprint = peerstate.secondary_verified_key_fingerprint.take();
        peerstate.verifier = peerstate.secondary_verifier.take();
        peerstate.fingerprint_changed = true;
        peerstate.save_to_db(&context.sql).await?;

        // Primary verified key changed.
        Ok(None)
    } else {
        Ok(None)
    }
}

/// Checks whether the message is allowed to appear in a protected chat.
///
/// This means that it is encrypted and signed with a verified key.
///
/// Also propagates gossiped keys to verified if needed.
async fn has_verified_encryption(
    context: &Context,
    mimeparser: &MimeMessage,
    from_id: ContactId,
    to_ids: &[ContactId],
) -> Result<VerifiedEncryption> {
    use VerifiedEncryption::*;

    // We do not need to check if we are verified with ourself.
    let to_ids = to_ids
        .iter()
        .copied()
        .filter(|id| *id != ContactId::SELF)
        .collect::<Vec<ContactId>>();

    if !mimeparser.was_encrypted() {
        return Ok(NotVerified("This message is not encrypted".to_string()));
    };

    // ensure, the contact is verified
    // and the message is signed with a verified key of the sender.
    // this check is skipped for SELF as there is no proper SELF-peerstate
    // and results in group-splits otherwise.
    if from_id != ContactId::SELF {
        let Some(peerstate) = &mimeparser.peerstate else {
            return Ok(NotVerified(
                "No peerstate, the contact isn't verified".to_string(),
            ));
        };

        let signed_with_verified_key = peerstate
            .verified_key_fingerprint
            .as_ref()
            .filter(|fp| mimeparser.signatures.contains(fp))
            .is_some();

        if !signed_with_verified_key {
            return Ok(NotVerified(
                "The message was sent with non-verified encryption".to_string(),
            ));
        }
    }

    mark_recipients_as_verified(context, from_id, to_ids, mimeparser).await?;
    Ok(Verified)
}

async fn mark_recipients_as_verified(
    context: &Context,
    from_id: ContactId,
    to_ids: Vec<ContactId>,
    mimeparser: &MimeMessage,
) -> Result<()> {
    if mimeparser.get_header(HeaderDef::ChatVerified).is_none() {
        return Ok(());
    }
    let contact = Contact::get_by_id(context, from_id).await?;
    for id in to_ids {
        let Some((to_addr, is_verified)) = context
            .sql
            .query_row_optional(
                "SELECT c.addr, LENGTH(ps.verified_key_fingerprint) FROM contacts c
                LEFT JOIN acpeerstates ps ON c.addr=ps.addr WHERE c.id=?",
                (id,),
                |row| {
                    let to_addr: String = row.get(0)?;
                    let is_verified: i32 = row.get(1).unwrap_or(0);
                    Ok((to_addr, is_verified != 0))
                },
            )
            .await?
        else {
            continue;
        };
        // mark gossiped keys (if any) as verified
        if let Some(gossiped_key) = mimeparser.gossiped_keys.get(&to_addr.to_lowercase()) {
            if let Some(mut peerstate) = Peerstate::from_addr(context, &to_addr).await? {
                // If we're here, we know the gossip key is verified.
                //
                // Use the gossip-key as verified-key if there is no verified-key.
                //
                // Store gossip key as secondary verified key if there is a verified key and
                // gossiped key is different.
                //
                // See <https://github.com/nextleap-project/countermitm/issues/46>
                // and <https://github.com/deltachat/deltachat-core-rust/issues/4541> for discussion.
                let verifier_addr = contact.get_addr().to_owned();
                if !is_verified {
                    info!(context, "{verifier_addr} has verified {to_addr}.");
                    if let Some(fp) = peerstate.gossip_key_fingerprint.clone() {
                        peerstate.set_verified(gossiped_key.clone(), fp, verifier_addr)?;
                        peerstate.backward_verified_key_id =
                            Some(context.get_config_i64(Config::KeyId).await?).filter(|&id| id > 0);
                        peerstate.save_to_db(&context.sql).await?;

                        let (to_contact_id, _) = Contact::add_or_lookup(
                            context,
                            "",
                            &ContactAddress::new(&to_addr)?,
                            Origin::Hidden,
                        )
                        .await?;
                        ChatId::set_protection_for_contact(
                            context,
                            to_contact_id,
                            mimeparser.timestamp_sent,
                        )
                        .await?;
                    }
                } else {
                    // The contact already has a verified key.
                    // Store gossiped key as the secondary verified key.
                    peerstate.set_secondary_verified_key(gossiped_key.clone(), verifier_addr);
                    peerstate.save_to_db(&context.sql).await?;
                }
            }
        }
    }

    Ok(())
}

/// Returns the last message referenced from `References` header if it is in the database.
///
/// For Delta Chat messages it is the last message in the chat of the sender.
async fn get_previous_message(
    context: &Context,
    mime_parser: &MimeMessage,
) -> Result<Option<Message>> {
    if let Some(field) = mime_parser.get_header(HeaderDef::References) {
        if let Some(rfc724mid) = parse_message_ids(field).last() {
            if let Some((msg_id, _)) = rfc724_mid_exists(context, rfc724mid).await? {
                return Message::load_from_db_optional(context, msg_id).await;
            }
        }
    }
    Ok(None)
}

/// Returns the last message referenced from References: header found in the database.
///
/// If none found, tries In-Reply-To: as a fallback for classic MUAs that don't set the
/// References: header.
async fn get_parent_message(
    context: &Context,
    references: Option<&str>,
    in_reply_to: Option<&str>,
) -> Result<Option<Message>> {
    let mut mids = Vec::new();
    if let Some(field) = in_reply_to {
        mids = parse_message_ids(field);
    }
    if let Some(field) = references {
        mids.append(&mut parse_message_ids(field));
    }
    message::get_by_rfc724_mids(context, &mids).await
}

pub(crate) async fn get_prefetch_parent_message(
    context: &Context,
    headers: &[mailparse::MailHeader<'_>],
) -> Result<Option<Message>> {
    get_parent_message(
        context,
        headers.get_header_value(HeaderDef::References).as_deref(),
        headers.get_header_value(HeaderDef::InReplyTo).as_deref(),
    )
    .await
}

/// Looks up contact IDs from the database given the list of recipients.
async fn add_or_lookup_contacts_by_address_list(
    context: &Context,
    address_list: &[SingleInfo],
    origin: Origin,
) -> Result<Vec<ContactId>> {
    let mut contact_ids = Vec::new();
    for info in address_list {
        let addr = &info.addr;
        if !may_be_valid_addr(addr) {
            continue;
        }
        let display_name = info.display_name.as_deref();
        if let Ok(addr) = ContactAddress::new(addr) {
            let (contact_id, _) =
                Contact::add_or_lookup(context, display_name.unwrap_or_default(), &addr, origin)
                    .await?;
            contact_ids.push(contact_id);
        } else {
            warn!(context, "Contact with address {:?} cannot exist.", addr);
        }
    }

    Ok(contact_ids)
}

#[cfg(test)]
mod receive_imf_tests;