Corrupted POP account crashing Mail in Leopard

Question

Hello all. After a full day of triage yesterday, I found that a single POP account is crashing the Mail app every time it tries to retrieve new mail. None of the other POP or IMAP accounts have any trouble sending or receiving when tested separately.
I had current backups for everything, so now I'm looking for guidance to repair / replace the damaged POP account.
If I delete that account or simply trash that mbox, is there a way to re-import that mbox from the backup copy? Will it fix the problem, or is it likely that either there's a corrupted message in the existing, downloaded mail OR a corrupted message on the server that's causing the problem?
Also, If I delete the offending POP account, which contains thousands of archival emails, will importing from the backup mean I have to wade through years of old email again? Now the messages are distributed across their respective projects in sub-folders. I'd prefer to have the archival material stay where it is.
As you may be able to tell, I'm trying to fix this with a surgical strike. I've had no trouble with Mail until yesterday, so I'm hoping to fix the problem with this one account and not waste another entire day.
Thanks for any pointers on this one,
Tim

Answer 1

"Very early in this topic I explain how to remove the old account folder, and then Import its mailboxes (after renaming a bit) to be On My Mailboxes accessible in the Sidebar. Once that is done, you can Move those messages back to any current account mailbox, such as Inbox or Sent. Was there something you did not understand about doing that?"
Unfortunately, I spent most of yesterday doing just that. I ended up not having all my email transfer - in some cases in was as few as 99 out of a 1,000 messages. The process seems imperfect, and it took a mixture of importing and re-importing mboxes and OS X Mail options in sequence to actually coax all the existing mail back.
"I suspect that the proper way to have proceeded was purging the com.apple.mail.plist all along. I can assure you from much experience that there are numerous instances where that is the real solution to such crashes, but you were reluctant to do that. I still would advise doing that, since corruption in any area we have discussed could result in a corruption of that plist file, and purging is often the only solution. Your test result with a New User Account is also an indicator of needing to purge and freshen the com.apple.mail.plist file."
My reluctance stems from prior nightmares trying to retrieve archival and current email after rebuilding com.apple.mail.plist files in earlier versions of Mail. My experience yesterday solidified that fear. If Apple had some retrieval / rebuild utility that matched the current numbers of messages from any given account (including draft, sent, inbox, etc.) and then came up with the same numbers of re-imported messages on the other end, I'd have a lot more confidence in the process. Instead, I went from 1,024 existing messages to 623 after re-creating the account.
Believe me, I'm very appreciative of your attention, but wiping out years worth of messages with very little expectation of ever getting the full complement back is daunting. I'm going to re-investigate Mail Steward and (one hopes) find a more stable way to archive important email outside the Mail app structure.
For now, I'll take your advice about dragging all the existing messages from the POP account and dragging them to their respective places in the new IMAP account. (I asked my most recent question because I've read elsewhere that dragging files from POP to IMAP accounts often results in incomplete transfers.)
I apologize if it seems I'm ungrateful and unwilling to take good advice. I've had more problems with Leopard than the past two iterations of OS X combined, and I'm annoyed by having to waste three full days trying to fix this 10.5.2 gremlin.
Thanks again,
Tim