Having a rather strange problem that I'm not quite sure how to work out.

Mail and iPhone are set up to receive emails, but not remove them from the server. the iPhone receives the mail without a problem, but Mail says it's receiving message x of x (at this point, it's up to 30 emails that it says it's retrieving). When it gets done "retrieving", NOTHING shows up! None of the e-mails come in....but they show up just fine on the iphone....any ideas?