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Composes e-mails from structured data

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

This is a standalone module that only generates raw e-mail source, you need to write your own or use an existing transport mechanism (SMTP client, Amazon SES, SendGrid etc). mailcomposer frees you from the tedious task of generating rfc822 compatible messages.

Build Status

See autogenerated docs here.

mailcomposer supports:

  • Unicode to use any characters ✔
  • HTML content as well as plain text alternative
  • Attachments and streaming for larger files (use strings, buffers, files or binary streams as attachments)
  • Embedded images in HTML
  • usage of your own transport mechanism


Install through NPM

npm install mailcomposer


Include mailcomposer module

var MailComposer = require("mailcomposer").MailComposer;

Create a new MailComposer instance

var mailcomposer = new MailComposer([options]);

Where options is an optional options object with the following possible properties:

  • escapeSMTP - if set replaces dots in the beginning of a line with double dots
  • encoding - sets transfer encoding for the textual parts (defaults to "quoted-printable")
  • keepBcc - if set to true, includes Bcc: field in the message headers. Useful for sendmail command.

Simple example

The following example generates a simple e-mail message with plaintext and html body.

var MailComposer = require("mailcomposer").MailComposer;
    mailcomposer = new MailComposer(),
    fs = require("fs");

// add additional header field
mailcomposer.addHeader("x-mailer", "Nodemailer 1.0");

// setup message data
    from: "",
    to: "",
    body: "Hello world!",
    html: "<b>Hello world!</b>"


// pipe the output to a file

The output for such a script (the contents for "test.eml") would look like:

MIME-Version: 1.0
X-Mailer: Nodemailer 1.0
Content-Type: multipart/alternative;

Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable

Hello world!
Content-Type: text/html; charset=utf-8
Content-Transfer-Encoding: quoted-printable

<b>Hello world!</b>


Add custom headers

Headers can be added with mailcomposer.addHeader(key, value)

var mailcomposer = new MailComposer();
mailcomposer.addHeader("x-mailer", "Nodemailer 1.0");

If you add an header value with the same key several times, all of the values will be used in the generated header. For example:

mailcomposer.addHeader("x-mailer", "Nodemailer 1.0");
mailcomposer.addHeader("x-mailer", "Nodemailer 2.0");

Will be generated into

X-Mailer: Nodemailer 1.0
X-Mailer: Nodemailer 2.0

The contents of the field value is not edited any way (except for the folding), so if you want to use unicode symbols you need to escape these to mime words by yourself.

Add message parts

You can set message sender, receiver, subject line, message body etc. with mailcomposer.setMessageOption(options) where options is an object with the data to be set. This function overwrites any previously set values with the same key

The following example creates a simple e-mail with sender being, receiver and plaintext part of the message as Hello world!:

    from: "",
    to: "",
    body: "Hello world!"

Possible options that can be used are (all fields accept unicode):

  • from (alias sender) - the sender of the message. If several addresses are given, only the first one will be used
  • to - receivers for the To: field
  • cc - receivers for the Cc: field
  • bcc - receivers for the Bcc: field
  • replyTo (alias reply_to) - e-mail address for the Reply-To: field
  • subject - the subject line of the message
  • body (alias text) - the plaintext part of the message
  • html - the HTML part of the message

This method can be called several times

mailcomposer.setMessageOption({from: ""});
mailcomposer.setMessageOption({to: ""});
mailcomposer.setMessageOption({body: "Hello world!"});

Trying to set the same key several times will yield in overwrite

mailcomposer.setMessageOption({body: "Hello world!"});
mailcomposer.setMessageOption({body: "Hello world?"});
// body contents will be "Hello world?"

Address format

All e-mail address fields take structured e-mail lists (comma separated) as the input. Unicode is allowed for all the parts (receiver name, e-mail username and domain) of the address. If the domain part contains unicode symbols, it is automatically converted into punycode, user part will be converted into UTF-8 mime word.

E-mail addresses can be a plain e-mail addresses

or with a formatted name

'Ноде Майлер' <>

Or in case of comma separated lists, the formatting can be mixed, 'Ноде Майлер' <>, "Name, User" <>

Add attachments

Attachments can be added with mailcomposer.addAttachment(attachment) where attachment is an object with attachment (meta)data with the following possible properties:

  • fileName (alias filename) - filename to be reported as the name of the attached file, use of unicode is allowed
  • cid - content id for using inline images in HTML message source
  • contents - String or a Buffer contents for the attachment
  • filePath - path to a file if you want to stream the file instead of including it (better for larger attachments)
  • streamSource - Stream object for arbitrary binary streams if you want to stream the contents (needs to support pause/resume)
  • contentType - content type for the attachment, if not set will be derived from the fileName property

One of contents, filePath or streamSource must be specified, if none is present, the attachment will be discarded. Other fields are optional.

Attachments can be added as many as you want.

Using embedded images in HTML

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 cid_value = + '.image.jpg';

var html = 'Embedded image: <img src="cid:' + cid_value + '" />';

var attachment = {
    fileName: "image.png",
    filePath: "/static/images/image.png",
    cid: cid_value

Start streaming

When the message data is setup, streaming can be started. After this it is not possible to add headers, attachments or change body contents.


This generates 'data' events for the message headers and body and final 'end' event. As MailComposer objects are Stream instances, these can be piped

// save the output to a file


Envelope can be generated with an getEnvelope() which returns an object that includes a from address (string) and a list of to addresses (array of strings) suitable for forwarding to a SMTP server as MAIL FROM: and RCPT TO:.

// {from:"", to:[""]}

NB! both from and to properties might be missing from the envelope object if corresponding addresses were not detected from the e-mail.

Running tests

Tests are run with nodeunit


npm test

or alternatively

node run_tests.js



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