Several months ago we mentioned that certain Linux distributions will, if they are running an SMTP server and accepting mail for local users, accumulate spam for “role” users who will never read their mail, e.g. mail, uucp, news, etc.
I finished by suggesting,
The best shortcut here is to bounce any email destined for the role users. This will vary depending on your MTA, so I won’t detail it here.
It’s true that it varies by MTA, but it turns out it’s really hard to find this information. MTAs aren’t set up to reject mail from specific addresses; they want a specific list of valid addresses and they’ll reject everything else.
It turns out that there’s a faster and cleaner method which is MTA-independent: lock the mailboxes for those users.
This could be as simple as putting an empty file in /var/spool/mail/uucp (for example) which is owned by root with 600 permissions, but that’s going to generate a bunch of error messages when your local delivery agent tries to write to a file it doesn’t have permissions for. A more elegant solution is to symlink those paths to /dev/null:
ln -s /dev/null /var/spool/mail/uucp
Now make sure the symlink has the correct ownership…
chown -h uucp:mail /var/spool/mail/uucp
Now all that spam will be silently delivered to the bit-bucket.
