WLM downloading more than once

I've used Windows Live Mail for years now, but lately have had problems with emails downloading that already have downloaded before. I've read online that a "bad" or corrupted email message may cause this; how do I find that email? Or is there some other way to fix this?

I partially solved this by going to Yahoo mail on the web and deleting old emails, but don't want to continue having to do this. BTW I am using POP3 for my email account. Only problem is with the Yahoo portion of my WLM account, Gmail and Outlook mail are ok.