How to disable mail receiving by local users without deleting their accounts
Update: Note that long after writing this guide, I've switched to Postfix as my mail server, so this guide was correct at the time of writing, it might be obsolete and/or incorrect at the time of reading.
On my server, sendmail is configured to receive mail for all local users.
And that includes "system" users, like root, backup, and mail.
So how can one forbid them to receive email, without deleting their accounts?
That's actually quite easy.
First, enable relevant sendmail feature: open the file /etc/mail/sendmail.mc
and add this line somewhere in it:
FEATURE(`blacklist_recipients')
After that, rebuild the actual sendmail config and restart sendmail:
cd /etc/mail; make; service sendmail restart
Second, edit /etc/mail/access file and add REJECT rules for them, like this:
backup@shpakovsky.ru REJECT
After that, rebuild the actual database:
makemap hash /etc/mail/access < /etc/mail/access
And last, test it: write an email to forbidden e-mail address and enjoy automated response from MAILER-DEMON :-)
More information regarding anti-spam protection you can find in the official sendmail documentation (archived version).