Not receiving anything in Mail.app inbox I have a Mac Pro, and I use Mail.app. Everything used to work fine with my POP account. 

However, last week my incoming mail showed that it was being downloaded to my inbox, but it never showed up. I have rebuilt my inbox, and also re-initiated, and configured my POP account, but the same problem remains.

I have also an IMAP account, which worked fine before and since this occurrence.

Any clue or hints on what is going on?
It's possible that your mailbox quota may have been exceeded, thus making it so you don't receive any new messages. If that's not the case, then I would completely remove the account from Mail or explore around ~/Library/Mail and edit/remove some files if necessary.