One of three things is happening:
1.) If you receive an email alerting you of a new PM, and you log into CP and don't see any new PM's, the person who sent you the PM most likely recalled it. This is only possible if they check the "Track PM" box prior to sending it.
2.) An old queue of emails was sent from the server. While this is rare, it happens... Sometimes emails don't make it out for whatever reason, and every once in awhile I'll log into the server and push out any pending emails.
3.) If you send someone a PM and they don't respond, they probably don't like you... :laugh:
On a side note, I'm going to be dropping the PM table of the database most likely just before I upgrade the forum. This will remove a ton of old PM's that are sitting in stagnant members' inboxes.
I will send a mass email to all members alerting them of the purge at least 1 week prior to the upgrade. You will have to archive any PM's you want to keep. Our PM table in the database is too large to convert over to the new PM system. Besides, like I said, there are thousands of PM's sitting in inboxes that are no longer needed.