mx-connect

Establish TCP connection to a MX server. This module takes a target domain or email address, resolves appropriate MX servers for this target and tries to get a connection, starting from higher priority servers.

Supports unicode hostnames and IPv6.

npm install mx-connect

Usage

const mxConnect = require('mx-connect');
mxConnect(options, callback);

Where

• options is the target domain, address, or configuration object
• callback is the function to run once connection is established to it fails

Example

This example establishes a connection to the MX of gmail.com and pipes output to console

const mxConnect = require('mx-connect');
mxConnect('user@gmail.com', (err, connection) => {
    if (err) {
        console.error(err);
    } else {
        console.log('Connection to %s:%s', connection.hostname, connection.port);
        // Connection to aspmx.l.google.com:25

        connection.socket.pipe(process.stdout);
        // 220 mx.google.com ESMTP k11-v6si869487ljk.7 - gsmtp
    }
});

Configuration options

You can use a domain name or an email address as the target, for additional configuration you would need to use configurtion object with the following properties (most are optional)

• target is either a domain name or an email address or an IP address or IP address literal (basically anything you can have after the @-sign in an email address). Unicode is allowed.

• port is the port number to connect to. Defaults to 25.

• localAddress is the local IP address to use for the connection

• localHostname is the hostname of the local address

• localAddressIPv4 is the local IPv4 address to use for the connection if you want to specify an address both for IPv4 and IPv6

• localAddressIPv6 is the local IPv6 address to use for the connection if you want to specify an address both for IPv4 and IPv6

• dnsOptions is an object for IP address related options

  • ignoreIPv6 (boolean, defaults to false) If true then never use IPv6 addresses for sending
  • preferIPv6 (boolean, defaults to false) If true then use IPv6 address even if IPv4 address is also available
  • blockLocalAddresses (boolean, defaults to false) If true then refuses to connect to IP addresses that are either in loopback, private network or attached to the server. People put every kind of stuff in MX records, you do not want to flood your loopback interface because someone thought it is a great idea to set 127.0.0.1 as the MX server

• mx is a resolved MX object or an array of MX objects to skip DNS resolving. Useful if you want to connect to a specific host.

  • exchange is the hostname of the MX
  • priority (defaults to 0) is the MX priority number that is used to sort available MX servers (servers with higher priority are tried first)
  • A is an array of IPv4 addresses. Optional, resolved from exchange hostname if not set
  • AAAA is an array of IPv6 addresses. Optional, resolved from exchange hostname if not set

• connectHook function (options, socketOptions, callback) is a function handler to run before establishing a tcp connection to current target (defined in socketOptions). If the socketOptions object has a socket property after the callback then connection is not established. Useful if you want to divert the connection is ome cases, for example if the target domain is in the Onion network then you could create a socket against a SOCK proxy yourself.

• connectError function (err, options, socketOptions) is a function handler to run when a connection to a MX fails.

Connection object

Function callback gets connection object as the second argument

• socket is a socket object against target
• hostname is the hostname of the exchange
• host is the IP address of the exchange
• port is the port used to connect
• localAddress is the local IP address used for the connection
• localPort is the local port used for the connection

License

EUPL v1.1 or newer