Mail Keeps Downloading the Same Emails

As of this morning, Mail (v4.5) keeps downloading the same emails over and over. I've got my delete setting to delete after one week (not immediately after download), but this has never been an issue before. In fact, I have multiple email accounts that access the same mail server, but only this one account is having this issue. I've gone in to my mailbox via Mail2Web and deleted all the messages in case it was some kind of corrupt email causing the issue. But as new emails come in, the problem reappears--the new emails are downloaded over and over. This is with a POP account.

I would think it'd be a server issue, not a Mail issue, but none of my other accounts that access the same mail server are affected. Any suggestions?