diff --git a/lib/Db/Message.php b/lib/Db/Message.php
index 47181897b5..ea27288b0a 100644
--- a/lib/Db/Message.php
+++ b/lib/Db/Message.php
@@ -261,6 +261,15 @@ public function setFlag(string $flag, bool $value = true) {
 	}
 
 	public function jsonSerialize() {
+		$tags = $this->getTags();
+		$indexed = array_combine(
+			array_map(
+				function (Tag $tag) {
+					return $tag->getImapLabel();
+				}, $tags),
+			$tags
+		);
+
 		return [
 			'databaseId' => $this->getId(),
 			'uid' => $this->getUid(),
@@ -277,7 +286,7 @@ public function jsonSerialize() {
 				'junk' => $this->getFlagJunk(),
 				'mdnsent' => $this->getFlagMdnsent(),
 			],
-			'tags' => $this->getTags(),
+			'tags' => $indexed,
 			'from' => $this->getFrom()->jsonSerialize(),
 			'to' => $this->getTo()->jsonSerialize(),
 			'cc' => $this->getCc()->jsonSerialize(),
diff --git a/lib/Db/Tag.php b/lib/Db/Tag.php
index b28149871e..261f9c393a 100644
--- a/lib/Db/Tag.php
+++ b/lib/Db/Tag.php
@@ -57,12 +57,12 @@ public function __construct() {
 	 */
 	public function jsonSerialize() {
 		return [
-			'databaseId' => $this->getId(),
+			'id' => $this->getId(),
 			'userId' => $this->getUserId(),
 			'displayName' => $this->getDisplayName(),
 			'imapLabel' => $this->getImapLabel(),
 			'color' => $this->getColor(),
-			'isDefaultTag' => $this->getisDefaultTag(),
+			'isDefaultTag' => $this->getIsDefaultTag(),
 		];
 	}
 }
diff --git a/lib/Db/TagMapper.php b/lib/Db/TagMapper.php
index 9a775223e4..2195902239 100644
--- a/lib/Db/TagMapper.php
+++ b/lib/Db/TagMapper.php
@@ -32,31 +32,22 @@
 use OCP\DB\QueryBuilder\IQueryBuilder;
 use OCP\IDBConnection;
 use OCP\IL10N;
-use Psr\Log\LoggerInterface;
 
 /**
  * @template-extends QBMapper<Tag>
  */
 class TagMapper extends QBMapper {
 
-	/** @var LoggerInterface */
-	private $logger;
-
 	/** @var IL10N */
 	private $l10n;
 
 	public function __construct(IDBConnection $db,
-								LoggerInterface $logger,
 								IL10N $l10n) {
 		parent::__construct($db, 'mail_tags');
-		$this->logger = $logger;
 		$this->l10n = $l10n;
 	}
 
 	/**
-	 * @param string $imapLabel
-	 * @return Entity
-	 *
 	 * @throws DoesNotExistException
 	 */
 	public function getTagByImapLabel(string $imapLabel, string $userId): Entity {
@@ -71,10 +62,6 @@ public function getTagByImapLabel(string $imapLabel, string $userId): Entity {
 	}
 
 	/**
-	 * @param integer $id
-	 * @param string $userId
-	 * @return Entity
-	 *
 	 * @throws DoesNotExistException
 	 */
 	public function getTagForUser(int $id, string $userId): Entity {
@@ -89,10 +76,7 @@ public function getTagForUser(int $id, string $userId): Entity {
 	}
 
 	/**
-	 * @param integer $id
-	 * @param string $userId
-	 * @return array
-	 *
+	 * @return Tag[]
 	 * @throws DoesNotExistException
 	 */
 	public function getAllTagForUser(string $userId): array {
@@ -105,12 +89,7 @@ public function getAllTagForUser(string $userId): array {
 		return $this->findEntities($qb);
 	}
 
-
 	/**
-	 * @param integer $id
-	 * @param string $userId
-	 * @return Entity
-	 *
 	 * @throws DoesNotExistException
 	 */
 	public function getTag(int $id): Entity {
@@ -124,14 +103,9 @@ public function getTag(int $id): Entity {
 	/**
 	 * Tag a message in the DB
 	 *
-	 * To tag (flag) a message on IMAP, @see OCA\Mail\Service\MailManager::tagMessage
-	 *
-	 * @param Tag $tag
-	 * @param string $messageId
-	 * @param string $userId
-	 * @return void
+	 * To tag (flag) a message on IMAP, @see \OCA\Mail\Service\MailManager::tagMessage
 	 */
-	public function tagMessage(Tag $tag, string $messageId, string $userId) {
+	public function tagMessage(Tag $tag, string $messageId, string $userId): void {
 		/** @var Tag $exists */
 		try {
 			$exists = $this->getTagByImapLabel($tag->getImapLabel(), $userId);
@@ -150,11 +124,9 @@ public function tagMessage(Tag $tag, string $messageId, string $userId) {
 	/**
 	 * Remove a tag from a DB message
 	 *
-	 * @param Tag $tag
-	 * @param string $messageId
-	 * @return void
+	 * This does not(!) untag a message on IMAP
 	 */
-	public function untagMessage(Tag $tag, string $messageId) {
+	public function untagMessage(Tag $tag, string $messageId): void {
 		$qb = $this->db->getQueryBuilder();
 		$qb->delete('mail_message_tags')
 			->where($qb->expr()->eq('imap_message_id', $qb->createNamedParameter($messageId)))
@@ -163,22 +135,22 @@ public function untagMessage(Tag $tag, string $messageId) {
 	}
 
 	/**
-	 * @param array $messages
-	 * @return array
+	 * @param Message[] $messages
+	 * @return Tag[][]
 	 */
-	public function getAllTagsForMessages(array $messages):array {
+	public function getAllTagsForMessages(array $messages): array {
 		$ids = array_map(function (Message $message) {
 			return $message->getMessageId();
 		}, $messages);
 
 		$qb = $this->db->getQueryBuilder();
-		$ids = $qb->select('mt.*')
+		$idsQuery = $qb->select('mt.*')
 			->from('mail_message_tags', 'mt')
 			->where(
 				$qb->expr()->in('imap_message_id', $qb->createNamedParameter($ids, IQueryBuilder::PARAM_STR_ARRAY))
 			);
-		$qb = $qb->execute();
-		$queryResult = $qb->fetchAll();
+		$idsQuery = $idsQuery->execute();
+		$queryResult = $idsQuery->fetchAll();
 		if (empty($queryResult)) {
 			return [];
 		}
@@ -199,12 +171,9 @@ public function getAllTagsForMessages(array $messages):array {
 	 * <i>The array_udiff can be removed and the insert warpped in
 	 * an exception as soon as NC20 is not supported any more</i>
 	 *
-	 * @param MailAccount $account
-	 * @return void
-	 *
 	 * @link https://github.com/nextcloud/mail/issues/25
 	 */
-	public function createDefaultTags(MailAccount $account) {
+	public function createDefaultTags(MailAccount $account): void {
 		$tags = [];
 		for ($i = 1; $i < 6; $i++) {
 			$tag = new Tag();
diff --git a/lib/Migration/Version1100Date20210304143008.php b/lib/Migration/Version1100Date20210304143008.php
index 261a6cf700..06c6f65782 100644
--- a/lib/Migration/Version1100Date20210304143008.php
+++ b/lib/Migration/Version1100Date20210304143008.php
@@ -112,7 +112,6 @@ public function changeSchema(IOutput $output, Closure $schemaClosure, array $opt
 	 * @param array $options
 	 */
 	public function postSchemaChange(IOutput $output, Closure $schemaClosure, array $options): void {
-		// repair step!
 		$accounts = $this->mailAccountMapper->getAllUserIdsWithAccounts();
 		foreach ($accounts as $account) {
 			$this->tagMapper->createDefaultTags($account);
diff --git a/lib/Model/IMAPMessage.php b/lib/Model/IMAPMessage.php
index 3318cb3af0..24743ef44b 100644
--- a/lib/Model/IMAPMessage.php
+++ b/lib/Model/IMAPMessage.php
@@ -752,8 +752,8 @@ public function toDbMessage(int $mailboxId, MailAccount $account): Message {
 	 *
 	 * @link https://github.com/nextcloud/mail/issues/25
 	 *
-	 * @param array $tags
-	 * @return array
+	 * @param string[] $tags
+	 * @return Tag[]
 	 */
 	private function generateTagEntites(array $tags, string $userId): array {
 		$t = [];