I ran "yum update" before bed last night to update my CentOS (RHEL) 5.2 system. Unfortunately, I didn't notice that email stopped flowing. Cyrus IMAPd was running, but no new mail was coming in. postfix was accepting mail, but new mail wasn't reaching Cyrus. Melissa let me know that mail wasn't working, and I discovered that again, the update had broken amavisd-new.

yum & rpm don't coexist well with cpan, and cpan itself has lots of trouble with Compress::Zlib. After a bunch of poking around, I eventually got cpan to reinstall (or just properly recognize?) Compress::Zlib, and got amavisd-new restarted; then postfix delivered the outstanding mail.

The whole cpan dance was prolonged and complicated by long cpan timeouts attempting to contact FTP mirrors -- presumably due to firewall restrictions that I never noticed because I avoid FTP. After a bunch of futzing with "o conf urrllist", I expunged the FTP mirrors and replaced them with HTTP mirrors; I was then eventually able to reinstall the necessary modules.