I just went through two weeks of hell with my MBP and finally diagnosed the problem: Mail Scripts. While I sincerely appreciate the developer's efforts and the need for this product (why doesn't Apple just build in a remove duplicates function?????), it caused major problems for me.

I was running 10.5.4 updated through Software Update and had just migrated to Mail.app (3.3). Everything was working fine, except I had all these duplicate emails after importing my Entourage mailboxes. I downloaded MailScripts, installed, and it worked fine in removing dupes, albeit very slowly.

My Mail.app started to hang at various times, on startup, on message open or close, at random times. My screen would freeze except for the cursor, and nothing would happen for up to 10 minutes, when then all of a sudden all the user actions would happen in rapid succession (moving a window, opening a message, closing it, typing characters). I had no time to wait so would do a hard restart. Any application that was open and being used would freeze if Mail was open, and it would happen within a few minutes after Mail.app was started.

Now, I never thought Mail Scripts was the issue, and proceeded to do the usual troubleshooting, with no success. The last resort was doing a clean install of 10.5.2 and then updating with the 10.5.4 stand-alone installer. I re-installed apps from downloads or CDs, not from my SuperDuper backup. Everything worked great and was super fast. This was a few days ago.

Yesterday night I was going through my mail and realized I had more dupes in some mailboxes. Then I realized that I didn't have Mail Scripts anymore with the clean install, so I downloaded and installed it, and removed my dupes. Shut down and called it a night.

This morning, booted up my MBP, opened Mail, and voila, within a few minutes, everything freezed. It was a sudden realization that Mail Scripts may be the problem, which I had not thought of at all before this point. After a few more tries and hard restarts, I trashed Mail Scripts (you have to trash them from two locations, in your root library, and your user library), and everything is fine now.

I mistakenly thought all my problems were due to MobileMe and the IMAP issues they've had. There may have been some overlap with the issues, but Mail Scripts was definitely the problem for me, using Leopard. Hopefully this post will help others who may be having the same issues.