Sometimes you may see an incoming message in the VPOP3 status, or know that someone has sent a message to you, but it is not arriving as expected.
There are many reasons this can happen, such as it being quarantined by the spam filter, or a configuration setting making the message go somewhere else.
Current versions of VPOP3 have a 'Message Trace' function where you can search for the message, by sender or subject, and VPOP3 will display the key decisions it made about that message, and where it went.
To use this facility, go to Settings -> Diagnostics -> Message Trace in the VPOP3 settings.