Mail 2.0.5 and MailTags
Here's another minor bump in the road that was discovered after installing Mac OS 10.4.3. I Heart Apple notes that Mail's behavior was a bit erratic after the update. Specifically, junk mail wasn't being consistently filtered, and some rules had stopped working. Furthermore, malfunctioning rules could not be edited, so fixing them seemed impossible.
After some searching, it was discovered that MailTags was the culprit. After updating to MailTags 1.1, all was right again. If you're running MailTags on Mac OS 10.4.3 (I love it myself), you may want to make sure you're using version 1.1.
[Via I Heart Apple]