npm i xd-smtp-connection



SMTP client module. Connect to SMTP servers and send mail with it.

This module is the successor for the client part of the (now deprecated) SMTP module simplesmtp. For matching SMTP server see smtp-server.

Build Status npm version

Other similar packages you might be interested in

  • nodemailer – all in one package to send email from Node.js
  • smtp-server – add SMTP server interface to your application
  • zone-mta – full featured outbound MTA built using smtp-connection and smtp-server modules


Install with npm

npm install smtp-connection

Require in your script

var SMTPConnection = require('smtp-connection');

Create SMTPConnection instance

var connection = new SMTPConnection(options);


  • options defines connection data

    • options.port is the port to connect to (defaults to 25 or 465)
    • options.host is the hostname or IP address to connect to (defaults to 'localhost')
    • options.secure defines if the connection should use SSL (if true) or not (if false)
    • options.ignoreTLS turns off STARTTLS support if true
    • options.requireTLS forces the client to use STARTTLS. Returns an error if upgrading the connection is not possible or fails.
    • options.opportunisticTLS tries to use STARTTLS and continues normally if it fails
    • options.name optional hostname of the client, used for identifying to the server
    • options.localAddress is the local interface to bind to for network connections
    • options.connectionTimeout how many milliseconds to wait for the connection to establish
    • options.greetingTimeout how many milliseconds to wait for the greeting after connection is established
    • options.socketTimeout how many milliseconds of inactivity to allow
    • options.logger optional bunyan compatible logger instance. If set to true then logs to console. If value is not set or is false then nothing is logged
    • options.debug if set to true, then logs SMTP traffic, otherwise logs only transaction events
    • options.authMethod defines preferred authentication method, e.g. 'PLAIN'
    • options.tls defines additional options to be passed to the socket constructor, e.g. {rejectUnauthorized: true}
    • options.socket - initialized socket to use instead of creating a new one
    • options.connection - connected socket to use instead of creating and connecting a new one. If secure option is true, then socket is upgraded from plaintext to ciphertext


SMTPConnection instances are event emitters with the following events

  • 'error' (err) emitted when an error occurs. Connection is closed automatically in this case.
  • 'connect' emitted when the connection is established
  • 'end' when the instance is destroyed


Establish the connection



  • callback is the function to run once the connection is established. The function is added as a listener to the 'connect' event.

After the connect event the connection has the following properties:

  • connection.secure - if true then the connection uses a TLS socket, otherwise it is using a cleartext socket. Connection can start out as cleartext but if available (or requireTLS is set to true) connection upgrade is tried


If the server requires authentication you can login with

connection.login(auth, callback)


  • auth is the authentication object

    • auth.user is the username
    • auth.pass is the password for the user
    • auth.xoauth2 is the OAuth2 access token (preferred if both pass and xoauth2 values are set) or an XOAuth2 token generator object.
  • callback is the callback to run once the authentication is finished. Callback has the following arguments

    • err and error object if authentication failed

If a XOAuth2 token generator is used as the value for auth.xoauth2 then you do not need to set auth.user. XOAuth2 generator generates required accessToken itself if it is missing or expired. In this case if the authentication fails, a new token is requeested and the authentication is retried. If it still fails, an error is returned.

XOAuth2 Example

var generator = require('xoauth2').createXOAuth2Generator({
    user: '{username}',
    clientId: '{Client ID}',
    clientSecret: '{Client Secret}',
    refreshToken: '{refresh-token}'

// listen for token updates
// you probably want to store these to a db
generator.on('token', function(token){
    console.log('New token for %s: %s', token.user, token.accessToken);

// login
    xoauth2: generator
}, callback);

Login using NTLM

smtp-connection has experimental support for NTLM authentication. You can try it out like this:

    domain: 'windows-domain',
    workstation: 'windows-workstation',
    user: 'user@somedomain.com',
    pass: 'pass'
}, callback);

I do not have access to an actual server that supports NTLM authentication so this feature is untested and should be used carefully.


Once the connection is authenticated (or just after connection is established if authentication is not required), you can send mail with

connection.send(envelope, message, callback)


  • envelope is the envelope object to use

    • envelope.from is the sender address

    • envelope.to is the recipient address or an array of addresses

    • envelope.size is an optional value of the predicted size of the message in bytes. This value is used if the server supports the SIZE extension (RFC1870)

    • envelope.use8BitMime if true then inform the server that this message might contain bytes outside 7bit ascii range

    • envelope.dsn is the dsn options

      • envelope.dsn.ret return either the full message 'FULL' or only headers 'HDRS'
      • envelope.dsn.envid sender's 'envelope identifier' for tracking
      • envelope.dsn.notify when to send a DSN. Multiple options are OK - array or comma delimited. NEVER must appear by itself. Available options: 'NEVER', 'SUCCESS', 'FAILURE', 'DELAY'
      • envelope.dsn.orcpt original recipient
  • message is either a String, Buffer or a Stream. All newlines are converted to \r\n and all dots are escaped automatically, no need to convert anything before.

  • callback is the callback to run once the sending is finished or failed. Callback has the following arguments

    • err and error object if sending failed

      • code string code identifying the error, for example 'EAUTH' is returned when authentication fails
      • response is the last response received from the server (if the error is caused by an error response from the server)
      • responseCode is the numeric response code of the response string (if available)
    • info information object about accepted and rejected recipients

      • accepted an array of accepted recipient addresses. Normally this array should contain at least one address except when in LMTP mode. In this case the message itself might have succeeded but all recipients were rejected after sending the message.
      • rejected an array of rejected recipient addresses. This array includes both the addresses that were rejected before sending the message and addresses rejected after sending it if using LMTP
      • rejectedErrors if some recipients were rejected then this property holds an array of error objects for the rejected recipients
      • response is the last response received from the server


Use it for graceful disconnect



Use it for less graceful disconnect



Use it to reset current session (invokes RSET command)




Jump To

Other similar packages you might be interested in
Create SMTPConnection instance
Login using NTLM