Since you’re running Dovecot, I’d recommend taking a look at Dovecot’s built-in Sieve support if you’re looking for an alternative to Procmail. This supports the ManageSieve protocol and so can be used even by users with no shell access with a compatible mail client (e.g. Thunderbird with the Sieve plugin). The rule syntax is significantly more human-friendly than procmail.
I have fond memories of Dovecot and Sieve from a couple of workplaces ago (not so much the qmail MTA and the 500-line Perl script run every single email that was used to handle OOO replies). IIRC I could use Sieve with Gnus there.