How to forward an e-mail address or a whole domain to /dev/null in Postfix

Last week I wrote about creating a catchall as well as forwarding all incoming e-mails in Postfix (NB: you might want to read that before going on with this post, as I’ll consider here that you already have working e-mail forwarding with the kind of config I used).
Now that I’ve used this to actually replace my Zoho forwarding, it is time to add some basic way to filter spam: I’m talking about not receiving spam to e-mail addresses I know I’ve never ever given as a receiving address. I’ve only got a few, notably do_not_reply/at/patheticcockroach.com, which I put as a sender on all automated e-mails generated from my sites, and yespopupV1@thesame, which I only used as a unique identifier for my Firefox extension Yes Popups. And stupid spammer bots think they are valid… okay, they were right… until now 😉

So, to stop receiving e-mails on those addresses, all I had to do was forward them to /dev/null. The problem is, it’s not possible put something like:
patheticcockroach@example.com /dev/null
in the Postfix alias file (/etc/postfix/virtual)

Instead, you have to create a system-wide alias, and then forward e-mails to it. So:
nano /etc/aliases
Then add a line such as:
devnull: /dev/null
(NB: you can chose whatever name you want instead of “devnull”, but I think that’s the most obvious and convenient one)
Then apply the changes (don’t forget that part or e-mails will bounce until you restart!):
newaliases

Now, you just need to configure Postfix to forward e-mails to user devnull. See the post I mentioned at the very beginning for details, long story short and considering that you already have some e-mail forwarding in place like my configuration:
nano /etc/postfix/virtual
add a line like:
patheticcockroach@example.com devnull
then apply:
postmap /etc/postfix/virtual
postfix reload

That’s all already. Don’t forget to test your setup though…

Additional note: if for some reason you have trouble setting-up system-wide aliases, as an alternative you can just use Webmin to create a user “devnull” with custom shell “/dev/null”. I tried it too, it seems to work just as well.

Sources:

• Dev Shed Forums – Postfix send mail to /dev/null – howto?
• ServerWatch Forwarding a Postfix Virtual Alias to /dev/null
• The Mad Philosopher – How to send an entire domain to /dev/null in Postfix