Compose E-Mail messages


mailcomposer is a Node.JS module for generating e-mail messages that can be streamed to SMTP or file.

NB! This module is not backwards compatible with versions 0.x

Install through NPM

npm install mailcomposer
var mailcomposer = require("mailcomposer");
var mail = mailcomposer(mailOptions);

Where mailOptions is an object that defines the components of the message, see below

To create a stream that outputs a raw rfc822 message from the defined input, use createReadStream()

var mail = mailcomposer({from: '...', ...});
var stream = mail.createReadStream();

To generate the message and return it with a callback use build()

var mail = mailcomposer({from: '...', ...});{

The following are the possible fields of an e-mail message:

  • from - The e-mail address of the sender. All e-mail addresses can be plain '' or formatted 'Sender Name <>', see here for details
  • sender - An e-mail address that will appear on the Sender: field
  • to - Comma separated list or an array of recipients e-mail addresses that will appear on the To: field
  • cc - Comma separated list or an array of recipients e-mail addresses that will appear on the Cc: field
  • bcc - Comma separated list or an array of recipients e-mail addresses that will appear on the Bcc: field
  • replyTo - An e-mail address that will appear on the Reply-To: field
  • inReplyTo - The message-id this message is replying
  • references - Message-id list (an array or space separated string)
  • subject - The subject of the e-mail
  • text - The plaintext version of the message as an Unicode string, Buffer, Stream or an object {path: '...'}
  • html - The HTML version of the message as an Unicode string, Buffer, Stream or an object {path: '...'}
  • watchHtml - Apple Watch specific HTML version of the message (experimental)
  • headers - An object or array of additional header fields (e.g. {"X-Key-Name": "key value"} or [{key: "X-Key-Name", value: "val1"}, {key: "X-Key-Name", value: "val2"}])
  • attachments - An array of attachment objects (see below for details)
  • alternatives - An array of alternative text contents (in addition to text and html parts) (see below for details)
  • envelope - optional SMTP envelope, if auto generated envelope is not suitable (see below for details)
  • messageId - optional Message-Id value, random value will be generated if not set
  • date - optional Date value, current UTC string will be used if not set
  • encoding - optional transfer encoding for the textual parts

All text fields (e-mail addresses, plaintext body, html body) use UTF-8 as the encoding. Attachments are streamed as binary.

Attachment object consists of the following properties:

  • filename - filename to be reported as the name of the attached file, use of unicode is allowed
  • cid - optional content id for using inline images in HTML message source
  • content - String, Buffer or a Stream contents for the attachment
  • encoding - If set and content is string, then encodes the content to a Buffer using the specified encoding. Example values: base64, hex, binary etc. Useful if you want to use binary attachments in a JSON formatted e-mail object.
  • path - path to a file or an URL (data uris are allowed as well) if you want to stream the file instead of including it (better for larger attachments)
  • contentType - optional content type for the attachment, if not set will be derived from the filename property
  • contentDisposition - optional content disposition type for the attachment, defaults to 'attachment'

Attachments can be added as many as you want.

var mailOptions = {
    attachments: [
        {   // utf-8 string as an attachment 
            filename: 'text1.txt',
            content: 'hello world!'
        {   // binary buffer as an attachment 
            filename: 'text2.txt',
            content: new Buffer('hello world!','utf-8')
        {   // file on disk as an attachment 
            filename: 'text3.txt',
            path: '/path/to/file.txt' // stream this file 
        {   // filename and content type is derived from path 
            path: '/path/to/file.txt'
        {   // stream as an attachment 
            filename: 'text4.txt',
            content: fs.createReadStream('file.txt')
        {   // define custom content type for the attachment 
            filename: 'text.bin',
            content: 'hello world!',
            contentType: 'text/plain'
        {   // use URL as an attachment 
            filename: 'license.txt',
            path: ''
        {   // encoded string as an attachment 
            filename: 'text1.txt',
            content: 'aGVsbG8gd29ybGQh',
            encoding: 'base64'
        {   // data uri as an attachment 
            path: 'data:text/plain;base64,aGVsbG8gd29ybGQ='

In addition to text and HTML, any kind of data can be inserted as an alternative content of the main body - for example a word processing document with the same text as in the HTML field. It is the job of the e-mail client to select and show the best fitting alternative to the reader. Usually this field is used for calendar events and such.

Alternative objects use the same options as attachment objects. The difference between an attachment and an alternative is the fact that attachments are placed into multipart/mixed or multipart/related parts of the message white alternatives are placed into multipart/alternative part.

Usage example:

var mailOptions = {
    html: '<b>Hello world!</b>',
    alternatives: [
            contentType: 'text/x-web-markdown',
            content: '**Hello world!**'

Alternatives can be added as many as you want.

All the e-mail addresses can be plain e-mail addresses

or with formatted name (includes unicode support)

"Ноде Майлер" <>

Notice that all address fields (even from) are comma separated lists, so if you want to use a comma in the name part, make sure you enclose the name in double quotes: "Майлер, Ноде" <>

or as an address object (in this case you do not need to worry about the formatting, no need to use quotes etc.)

    name: 'Майлер, Ноде',
    address: ''

All address fields accept comma separated list of e-mails or an array of e-mails or an array of comma separated list of e-mails or address objects - use it as you like. Formatting can be mixed.

to: ', "Ноде Майлер" <>, "Name, User" <>',
cc: ['', '"Ноде Майлер" <>, "Name, User" <>'],
bcc: ['', {name: 'Майлер, Ноде', address: ''}]

You can even use unicode domains, these are automatically converted to punycode

'"Unicode Domain" <info@müriaad-polü>'

SMTP envelope is usually auto generated from from, to, cc and bcc fields but if for some reason you want to specify it yourself, you can do it with envelope property.

envelope is an object with the following params: from, to, cc and bcc just like with regular mail options. You can also use the regular address format, unicode domains etc.

mailOptions = {
    from: '',
    to: '',
    envelope: {
        from: 'Daemon <>',
        to: ', Mailer <>'

Not all transports can use the envelope object, for example SES ignores it and uses the data from the From:, To: etc. headers.

Attachments can be used as embedded images in the HTML body. To use this feature, you need to set additional property of the attachment - cid (unique identifier of the file) which is a reference to the attachment file. The same cid value must be used as the image URL in HTML (using cid: as the URL protocol, see example below).

NB! the cid value should be as unique as possible!

var mailOptions = {
    html: 'Embedded image: <img src=""/>',
    attachments: [{
        filename: 'image.png',
        path: '/path/to/file',
        cid: '' //same cid value as in the html img src