I have two separate e-mail addresses. One is my main address and one is my confidential address. I can receive mail on the confidential address but am all of a sudden getting an error receiving on my main address. The error message states that there was a failure to log onto incoming POP3 mail server because my mailbox on the server is in use?

What the heck?

Don't know if this is the fix, but I've seen this happen on a mail server when an incoming message is corrupt and there is no -end of file- tag. The account on the server just sits there and looks stupid waiting for the end of file which never comes, and it can keep the account connection open indefinitely.

You should be able to call your ISP and have them check your mailbox, the most recent file is likely really big and they can just delete it and all should start working again.

That must have been the problem. I logged onto my e-mail via Comcast. There was one e-mail in there that appeared to be spam that got through the filter. I didn't recognize the sender and the subject line was odd. After deleting that off the server, my e-mails all started coming right through.