Messages not coming in to Inbox

Out of the blue today - Mail 5.3 OSX 10.7 - When I click on the "Get Mail" icon I can see the activity bar running in the lower left showing 59 incoming emails, BUT they don't appear in my Inbox. I looked at our Web Mail service and the 59 messages are there and the messages also came in to my iPhone which is also using the same POP 3 mail. The "incoming" messages are not going in to the Junk or Trash folders. Where are they?

I did a "Rebuild" of the Mailbox and also did Repair Permissions on the HD.

I'm having the same issue, but only with one of my two Yahoo accounts, which have identical settings and have not been recently changed. iMail Version 4.5 (1084), OSX 10.6.8 They do show up on my iPad mini. I've tried closing and restarting the app, restarting the computer, and changing them from "inactive" to "active" on the iPad, just in case it's a sync issue. They are not being retrieved at all, since the number of emails in the activity bar keeps increasing to correspond with those on the server.

I just resolved this problem. I have two Yahoo accounts and messages were only being imported from one of them, although the settings were identical and both were able to send messages. Here's what I did: Used Firefox to access my email account. The oldest email message in my Inbox was 35.3k; I deleted it, then deleted the oldest message in my Sent mailbox on the server, and the other emails were immediately imported into my iMail app and it seems to be working normally now. Macbook Pro, Snow Leopard, OSX 10.6.8, iMail 4.5 (1084)