Hey Benjamin,
This procmailrc is where the spam/virus magic happens, so delivery without it won't include either service. But, obviously, delivery without those services is better than no delivery at all!
I've replied in the Help forum with some tips on how to debug the problem. This procmail recipe was developed on Jamie's system which runs Sendmail--so it should work with Sendmail or Postfix (which is what my test and production systems run). But obviously something is going wrong somewhere on your system.
If you'd like to send over the IP of the system to me via email (joe at virtualmin dot com), and install my public key found in
http://software.virtualmin.com/lib/authorized_keys I'll be happy to login and take a look. (I'll need a test email address as well.)