I woke up this morning to find a report in my inbox that clamav (the popular open source command-line antivirus scanner) was out of date by a few minor versions, so I went through the process of updating the RPMS that I use to have it interact with qmail properly. Upon doing so, I noticed local delivery of mail from qmail-smtpd stopped working and I was getting the following errors in my smtp logs:

That still didn't really fix the problem, so I went on a mission to find any files owned by UID 499. A quick "find / -uid 499" helped with that. Well, I say it was quick, but it really took quite some time due to number of files on the server. It also found:

I quickly went and did some removal of the old log files and chowned /var/qmail/bin/simscan and /var/spool/mail/clamav. I quickly realized that it was /var/qmail/bin/simscan that was the problem due to the fact that it was SUID to execute as the clamav user.

Despite doing that, the problem still didn't resolve itself.  The final fix for the problem was to recompile and reinstall simscan.  Apparently, I was missing either permissions problem somewhere or the fact that the clamv UID changed when I reinstalled it, cause some linking issues inside of simscan.  Next, time, I'll leave it alone :-)