Postfix: For a certain address, only allow emails from a certain domain

Question

I've set up my server so that, in order to track down the source of spam (and block it), the email address that I use to sign up for stuff is [email protected] (e.g. for Facebook, it would be [email protected]).

Now, suppose that I get spam emails to [email protected] - (from, e.g., [email protected]). I'd like to block them, but continue to receive emails from the facebook.com domain - i.e. I would like to restrict email to a certain address to come from a certain domain.

Is this possible with Postfix? Or will I need something additional? (I'm already running Dovecot, although that doesn't seem like the right tool).

I'm not using a conventional spam filter because the above seems more elegant - however, if there is a spam filter that can implement the above, I'd be happy to use it.

Answer 1

Haraka can handle this case easily, and it's very easy to setup in front of Postfix so that your current Postfix setup continues to work as-is (or if you don't want to do that, it can deliver direct to Dovecot via LMTP).

You'd setup a Haraka plugin like the following:

var net_utils = require('./net_utils');

exports.hook_rcpt = function (next, connection, params) {
    var recip = params[0];
    if (connection.relaying) {
        // Already relaying (i.e. outbound) - skip.
        return next();
    }

    // Get who this is coming from and change a.b.example.com into just example.com
    var check_domain = net_utils.get_organizational_domain(connection.transaction.mail_from.host);

    // Turn 'example.com' into just 'example'
    check_domain = check_domain.replace(/\..*$/, '');

    if (check_domain.toLowerCase() != recip.user.toLowerCase()) {
        return next(DENY, "You dirty dirty spammer");
    }

    next();
}

Add that to your plugins directory, and add a line to config/plugins specifying what you called the file so that it is loaded into your configuration.