posted on Sat, Sep 07 '24 under tag:

Have you ever had a mailu server keep retrying mails to email addresses that don’t exist? What if you didn’t want to or didn’t have access to stop emails to this address at the source?

If you have a setup like this:

Application A -> Mailu based mailserver M -> non-existent recipient R

And your application keeps sending emails to R (let’s say “notification” emails).

And you do not want to configure A to stop sending (or A doesn’t have the feature to block emails to particular addresses.)

Then what you can do is the following.

Transport.map of postfix to the rescue

transport is a mechanism that allows postfix to pattern-match To addresses and decide what to do with the emails.

If you want to discard emails being sent to “user@example.com”, you can edit /var/mailu/overrides/postfix/transport.map to include this line:

user@example.com discard:

(Do notice there’s a colon (:) at the end of discard)

This tells postfix to send the emails to user@example.com to the discard transport. (Something like piping to /dev/null)

If you want to block emails to an entire domain (say one that’s expired), you can do:

example.com discard:

You might have to restart the smtp service for changes to be picked up.

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