diff --git a/README.md b/README.md
index 86efeb4..17b8afe 100644
--- a/README.md
+++ b/README.md
@@ -61,7 +61,12 @@ Otherwise you will need to install XCode from the [App Store][app-store] or [App
 
 > **NOTE**: You should probably just use [email-templates][] directly instead of using this package.
 
-The function `previewEmail` returns a `Promise` which resolves with a URL. We automatically open the browser to this URL unless you specify `options.open` as `false` (see [Options](#options) for more info).
+The function `previewEmail` accepts two arguments `message` and `options`, and it returns a `Promise` which resolves with a URL (unless you specify `returnHTML: true` in `options` argument).  We automatically open the browser to this URL unless you specify `options.open` as `false` (see [Options](#options) for more info).
+
+* The argument `message` can be one of the following:
+  * `Object` – A [Nodemailer message configuration](https://nodemailer.com/message/) object.
+  * `String` or `Buffer` – A custom generated RFC822 formatted message to use (instead of one that is generated by Nodemailer – see [Nodemailer's custom source](https://nodemailer.com/message/custom-source/)).
+* The argument `options` is documented under [Options](#options) below.
 
 ```js
 const previewEmail = require('preview-email');
diff --git a/index.js b/index.js
index 58bf285..2a5e319 100644
--- a/index.js
+++ b/index.js
@@ -5,6 +5,7 @@ const os = require('os');
 const path = require('path');
 const process = require('process');
 const util = require('util');
+const { Buffer } = require('buffer');
 const displayNotification = require('display-notification');
 const getPort = require('get-port');
 const nodemailer = require('nodemailer');
@@ -13,7 +14,6 @@ const pEvent = require('p-event');
 const pWaitFor = require('p-wait-for');
 const pug = require('pug');
 const uuid = require('uuid');
-const { Iconv } = require('iconv');
 const { isCI } = require('ci-info');
 const { simpleParser } = require('mailparser');
 
@@ -40,17 +40,22 @@ const previewEmail = async (message, options) => {
     simpleParser: {},
     ...options
   };
-  debug('message', message, 'options', options);
 
-  if (typeof message !== 'object')
-    throw new Error('Message argument is required');
+  debug('message', message, 'options', options);
 
-  const response = await transport.sendMail(message);
+  let raw;
+  if (Buffer.isBuffer(message)) {
+    raw = message;
+  } else if (typeof message === 'string') {
+    raw = message;
+  } else if (typeof message === 'object') {
+    const response = await transport.sendMail(message);
+    raw = response.message;
+  } else {
+    throw new TypeError('Message argument is required');
+  }
 
-  const parsed = await simpleParser(response.message, {
-    ...options.simpleParser,
-    Iconv
-  });
+  const parsed = await simpleParser(raw, options.simpleParser);
 
   const html = await renderFilePromise(
     options.template,
@@ -152,7 +157,7 @@ const previewEmail = async (message, options) => {
       });
 
       const emlFilePath = `${options.dir}/${options.id}.eml`;
-      await writeFile(emlFilePath, response.message);
+      await writeFile(emlFilePath, raw);
       debug('emlFilePath', emlFilePath);
       const xcrun = childProcess.spawn('xcrun', [
         'simctl',
diff --git a/package.json b/package.json
index a239069..261bdfd 100644
--- a/package.json
+++ b/package.json
@@ -15,7 +15,6 @@
     "display-notification": "2.0.0",
     "fixpack": "^4.0.0",
     "get-port": "5.1.1",
-    "iconv": "^3.0.1",
     "mailparser": "^3.6.4",
     "nodemailer": "^6.9.2",
     "open": "7",