[tamarian]

I'm not sure how this would work, due to my lack of knowledge with qmail.

Does qmail use spool files? Check what's there in your /var/spool/mail.

If not, does qmail allow .forward files? If so, have the .forward create a spool file

example of .forward contents
~/home/myuser/mail/bounces

With this, you create your own spool file, and use it in the script. (warning: make sure you regularly clean this file, as bounce spools can get very large, very quickly with many forum users)

These are just off the top of my head, as I don't know how qmail works, I'm a postfix user.