This idea has been merged into another idea. To comment or vote on this idea, please visit DOMINO-I-409 Implement greylisting to domino smtp.
Graylisting is a way to deter incoming spam.
" A mail transfer agent (MTA) using greylisting will "temporarily reject" any email from a sender it does not recognize. If the mail is legitimate, the originating server will try again after a delay, and if sufficient time has elapsed, the email will be accepted."