This is directed to phoenix --
I researched out postgrey. Not bad, actually! I wonder if I could use this instead of TMDA. I'll have to think about that a bit. The only problem that I can think of now is that my current TMDA setup allows for a "pending messages" folder. Rather than actually completely rejecting the message, can postgrey actually accept the message if it's to a valid recipient address, but notify the sender of the temporary rejection, and put the email in some sort of pending location while it waits for the response from the sending MTA? That way, a user could optionally get their delayed message immediately.