mail-io

This module provides an easy way to implement your own SMTP server. It supports plugins and can be easily extended.

It also supports mail relay features.

usage

You can create a server like this:

// Load the module
const mio = require('mail-io');

// Create a new SMTP server
const server = new mio.Server({ ... options ... });

// Listen for new client connections
server.on('session', (session) => {
	
	// Register a custom authentication handler
	session.on('auth', (req, res) => {
		
		// Only accept user "john" with password "doe"
		if (req.user && req.user.username === 'john' && req.user.password === 'doe') {
			return res.accept(250, 'OK');
		} else {
			return res.reject(535, 'Authentication failed');
		}
		
	});
	
});

// Register a global handler to reject all recipients that do not belong
// to "foo.com" domain
server.addHandler('rcpt', {
	name: 'my-rcpt-handler',
	before: 'dnsbl',
	handler: (req, res) => {
		
		if (req.to.split('@')[1] === 'foo.com') {
			res.accept();
		} else {
			res.reject(502, 'We only accept mail for the "foo.com" domain');
		}
		
	}
});

// Listen on port 25
server.listen(25);

command handlers

You can register command handlers with session.on('command', function(req, res) {...}) for any command, which will get called when the command is issued by the client and previous handlers (if any) have accepted the request. In the background, the handler will be pushed to the end of the handler queue, so it will only get called if all previous handlers for this command accepted with res.accept. Note that the core plugin always gets precedence over any other plugins, which makes sure that internally used plugins execute first.

A command handler is a function that gets passed two objects, req and res.

req object

The req object contains the issued command and the data, information about the session and the plugin specific configuration (if provided). The req object is shared between all handlers of the same command. It contains the following attributes:

command

the commandobject contains the cmd property which contains the name of the command in lowercase letters, e.g. mail or rcpt. It also contains a data property which is a string that contains the data that came after the command.

session

the session object is initialized upon a client connection and is shared between all handlers. It contains the following attributes:

id: a unique id for every client session
transaction: the id of the current transaction, starting at 0 and getting increased after every successful data command
accepted: a map that contains all commands as the key that have been accepted. The value is the status code. NOTE this is very useful to check if a command has been completed
rejected: same as accepted, but for commands that have been rejected
envelope: a map that contains the mail envelope data, like to *(array)* and from *(string)*
client: an object containing information about the connected client, like address and hostname
config: a reference to the options passed to the createServer constructor
connection: the underlying smtp-stream connection. connection.socket contains the raw net socket of the connection.
handlers: a map that contains all registered command handlers. You shouldn't have to mess around with it, but just in case :)
data: a map containing the commands as the key and a map of handlers as the value, which in turn contain the data that was set using res.set. You should not access this data directly and rather use res.get to obtain the data
secure: a boolean indicating if the connection is using TLS.
counters: a map of counters that are used internally to track failed login and command attempts
log: a map that contains logging functions for different levels. You should NOT use this and rather use res.log instead.

config

Contains the handler specific configuration that was passed via the options in the createServer constructor. For example, to pass a custom DNSBL blacklist server to rcpt/dnsbl plugin, the options object may look like this:

const server = new mio.Server ({
	plugins: {
		'rcpt/dnsbl': {
			blacklist: 'zen.spamhaus.org'
		}
	}
}, function() {...})

more

Some core plugins extend the req object, so you may have additional data available on the req object. For example the auth/core plugin adds req.user to the request if the auth request was completed successfully. mail/core adds req.from and rcpt/core adds req.to.

res object

The res object contains methods that can be used to respond to the command, and to add additional information to the session. IMPORTANT You MUST call either res.accept, res.reject or res.end exactly once during the execution of your handler code, otherwise the connection will be left hanging.

It contains the following methods:

accept(<code>, <message>)

Accepts the request. You can pass an optional response code and message which will be used when sending the response to the client. Note that if there are remaining handlers for this command, they will be called afterwards and may also change the code and message, or even reject the request. This means that accepting a request with res.accept does not guarantee that this response will be sent to the client as is. If you do not pass a response code or message, the default code is 250 and the default message is OK

reject(code, message)

If you reject a request, the response is immediately sent to the client and no more handlers for this command will be executed. You MUST to provide a code and a message when you reject. You should make sure that the code is appropriate for the command you are rejecting, otherwise, the client may misunderstand your answer.

end(<code>, <message>)

When calling end, the connection to the client will be closed. No more command handlers will be executed. You can pass an optional code and message to the end method, which will write the response to the client before closing the connection.

write(message)

In some situations it is required to send a message to the client. For example, the ehlo commands sends a list of supported features to the client before accepting the request. Write does not end the current command handler and you are still required to either accept, reject or end the request before the execution can continue.

read(callback)

Sometimes, you may need additional information from the client (see auth/core) that has to be read within the same command handler. For this case, use res.read and provide a callback function, that will be called back with the data received from the client.

set(data)

If you want to share data with other handlers, set will allow you to do that. You can pass any data, which other handlers can get using res.get.

get(handler)

If you want to access data from another command handler, you can use get. handler is a string that accepts two flavors:

command: gets all stored data for a specific command. The returned object will be a map containing the name of the handler as the key and their stored data as the value.
command/handler: returns the data stored by that handler

As an example, the spamd plugin is registered to the queue command. When it receives a spam score, it will be saved using res.set(score). If you want to access that data, you could call res.get('queue/spamd'), which would directly return the score, or you could call res.get('queue') which would return an object with spamd as a key and the score as the value.

Note: you can also access the same data via req.session.data.queue.spamd.

log <object>

res.log is an object that contains functions for the logging levels info, warn, error, verbose and debug. If you want to log some information, you should use these logging functions. They accept a message as the first argument and any data as the following arguments, that will be printed as separate lines using util.inspect.

mofux/mail-io

mail-io

usage

command handlers

req object

res object