Unable to lock mailbox

Fandt følgende:

A POP mailbox can only be accessed by one incoming connection at a time. If your mail checker has already logged in to your email account, your email program cannot get access to the same account at the same time. In such cases, when the mailbox is already locked by another process, the POP server returns: "-ERR unable to lock mailbox".

Men hvordan skal jeg så finde det program, som anvender den mailbox?

Løste det selv - slettede blot mailboxen og oprettede den igen. Nu virker det.