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Simple SMTP server/client module
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This is a module to easily create custom SMTP servers - use SMTP as a first class protocol in Node.JS!

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SMTP Server


Create a new SMTP server instance with

var smtp = new simplesmtp.createServer([options]);

And start listening on selected port

smtp.listen(25, [function(err){}]);

SMTP options can include the following:

  • HOSTNAME - the hostname of the server, will be used for informational messages
  • debug - if set to true, print out messages about the connection
  • timeout - client timeout in milliseconds, defaults to 60 000 (60 sec.)
  • secureConnection - start a server on secure connection
  • SMTPBanner - greeting banner that is sent to the client on connection
  • requireAuthentication - if set to true, require that the client must authenticate itself
  • validateSender - if set to true, emit 'validateSender' with email and callback when the client enters MAIL FROM:<address>
  • validateRecipients - if set to true, emit 'validateRecipient' with email and callback when the client enters RCPT TO:<address>
  • maxSize - maximum size of an e-mail in bytes (currently informational only)
  • credentials - TLS credentials ({key:'', cert:'', ca:''}) for the server
  • authMethods - allowed authentication methods, defaults to ["PLAIN", "LOGIN"]
  • disableEHLO - if set to true, support HELO command only


var simplesmtp = require("simplesmtp"),
    fs = require("fs");

var smtp = new simplesmtp.createServer();

smtp.on("startData", function(envelope){
    console.log("Message from:", envelope.from);
    console.log("Message to:",;
    envelope.saveStream = fs.createWriteStream("/tmp/message.txt");

smtp.on("data", function(envelope, chunk){

smtp.on("dataReady", function(envelope, callback){
    console.log("Incoming message saved to /tmp/message.txt");
    callback(null, "ABC1"); // ABC1 is the queue id to be advertised to the client
    // callback(new Error("That was clearly a spam!"));


  • startData (envelope) - DATA stream is opened by the client (envelope is an object with from, to, host and remoteAddress properties)
  • data (envelope, chunk) - e-mail data chunk is passed from the client
  • dataReady (envelope, callback) - client is finished passing e-mail data, callback returns the queue id to the client
  • authorizeUser (envelope, username, password, callback) - will be emitted if requireAuthentication option is set to true. callback has two parameters (err, success) where success is Boolean and should be true, if user is authenticated successfully
  • validateSender (envelope, email, callback) - will be emitted if validateSender option is set to true
  • validateRecipient (envelope, email, callback) - will be emitted it validataRecipients option is set to true

SMTP Client


SMTP client can be created with simplesmptp.connect(port[,host][, options]) where

  • port is the port to connect to
  • host is the hostname to connect to (defaults to "localhost")
  • options is an optional options object (see below)

Connection options

The following connection options can be used with simplesmtp.connect:

  • secureConnection - use SSL
  • name - the name of the client server
  • auth - authentication object {user:"...", pass:"..."}
  • ignoreTLS - ignore server support for STARTTLS
  • debug - output client and server messages to console
  • instanceId - unique instance id for debugging (will be output console with the messages)

Connection events

Once a connection is set up the following events can be listened to:

  • 'idle' - the connection to the SMTP server has been successfully set up and the client is waiting for an envelope
  • 'message' - the envelope is passed successfully to the server and a message stream can be started
  • 'ready' (success) - the message was sent
  • 'rcptFailed' (addresses) - not all recipients were accepted (invalid addresses are included as an array)
  • 'error' (err) - An error occurred. The connection is closed and an 'end' event is emitted shortly
  • 'end' - connection to the client is closed

Sending an envelope

When an 'idle' event is emitted, an envelope object can be sent to the server. This includes a string from and an array of strings to property.

Envelope can be sent with client.useEnvelope(envelope)

client.on("idle", function(){
        from: "",
        to: ["", ""]

The to part of the envelope includes all recipients from To:, Cc: and Bcc: fields.

If setting the envelope up fails, an error is emitted. If only some (not all) recipients are not accepted, the mail can still be sent but an rcptFailed event is emitted.

client.on("rcptFailed", function(addresses){
    console.log("The following addresses were rejected: ", addresses);

If the envelope is set up correctly a 'message' event is emitted.

Sending a message

When 'message' event is emitted, it is possible to send mail. To do this you can pipe directly a message source (for example an .eml file) to the client or alternatively you can send the message with client.write calls (you also need to call client.end() once the message is completed.

If you are piping a stream to the client, do not leave the 'end' event out, this is needed to complete the message sequence by the client.

client.on("message", function(){

Once the message is delivered a 'ready' event is emitted. The event has an parameter which indicates if the message was transmitted( (true) or not (false).

client.on("ready", function(success){
        console.log("The message was transmitted successfully");

Closing the client

By default the client tries to keep the connection up. If you want to close it, run client.quit() - this sends a QUIT command to the server and closes the connection




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