Hi, Just begun playing around with GreyListing. It is another anti-spam technique. Simply said, what it does is: It is based on tuplets (sender, recipient, originating IP). The first time a server receives a message of one specific tuplet, it says to the originating server : I don't accept your message now, please come back a bit later. Real e-mail servers usually respect this and retry a few (typically 15) minutes later. When the server retries, the delays don't apply and the message is accepted. Then, the tuplet is added to a database (held in memory, dumped once in a while on disk), so that this tuplet is not subject to greylisting (delays) for a given period Spambots, zombie infected computers don't retry, so a lot of spam is denied just there, no more processing is needed. The benefits are two-fold There is less spam in the users' mailboxes There is less load on mail servers. Effectively, most servers use anti-spam software that uses a lot of resources (ne...