Mail crashes when trying to access pop accounts

Question

Help!
Since I updated to OS 10.4.8, mail has stopped working properly. Whenever I try to get mail from my pop accounts, it crashes immediately. As long as I stay offline, the program seems to work.
I tried deleting my accounts and re-entering them, but that didn't have any effect. Has anyone else had this problem? Does anyone know how to fix it?
Powerbook G4 12"   Mac OS X (10.4.8)  

Answer 1

You're welcome.
There is probably some corruption in one or more of the files used by the junk filter. The following procedure thoroughly gets rid of all those files, so that Mail creates them anew:
1. Quit Mail if it's running.
2. In the Finder, go to ~/Library/Mail/.
3. Locate LSMMap2 and move it to the Trash. This file stores information about what does and doesn't constitute junk, and is what allows the junk filter to learn. Clicking the Reset button in Preferences > Junk Mail also deletes LSMMap2. The file was called just LSMMap in early versions of Mail, delete that as well if you see it.
4. Locate DefaultCounts and move it to the Trash. This file keeps statistics about the number of messages that have been marked as junk, either automatically by the junk filter or manually by the user.
5. Locate MessageRules.plist and move it to the Desktop. This is where Mail 2.x stores all rules, including those used by the junk filter. If there is a file called MessageRules.plist.backup, move it to the Desktop too. You may also see MessageSorting.plist files there; this is where Mail 1.x stored the rules, and they are no longer used by Mail 2.x, so just move them to the Trash if you see them.
6. Look for the account folders. The name of each account folder starts with the account type (POP, IMAP, Mac), followed by the account username and the incoming mail server. Open each of the account folders, locate the Junk.mbox or Junk.imapmbox folder within it, and move it to the Trash if present.
7. Go to ~/Library/Mail/Mailboxes/. Locate any Junk.mbox folders there (their name may include the account name in parenthesis), and move them to the Trash.
Note: Messages in Junk folders with an .mbox suffix are stored locally and will be lost forever as a result of doing steps 6 and 7. If there is a chance that you have legit messages there that you want to preserve, either move the messages to another mailbox in Mail first, or move the Junk.mbox folder to the Desktop (to be imported back later) instead of to the Trash. Junk folders with an .imapmbox suffix aren't a concern because they are stored on the server and Mail will rebuild them automatically.
8. Open Mail. As a result of removing the rules file, the junk filter will be disabled now. You may want to either tell Mail to go offline immediately after opening it, or shut down the Internet connection before opening Mail, to prevent it from downloading anything until the junk mail filter has been enabled again.
9. Go to Mail > Preferences > Junk Mail, enable junk filtering, and configure it however you wish.
10. Go online again if you went offline in step 8.
If the above solves the problem and you don't have any rules you'd like to preserve or recreating them is not a daunting task, just delete the MessageRules.plist files that were moved to the Desktop and be done with it.
Note: For those not familiarized with the ~/ notation, it refers to the user's home folder. You can easily locate any of the folders referred to in this post by copying the file path here, doing Go > Go to Folder in the Finder, and pasting the file path there.