Published at LXer:

Traditional methods of spam protection involve using Bayesian detection rules (usually via SpamAssassin) on messages after they have been accepted by your server. Most mail sysadmins may have encountered the constant cries from their users asking “can’t you stop them sending it?”. Of course you can’t stop somebody sending a message but you can stop accepting them in the first place. Enter greylisting. These two articles are kind of follow-ons to my previous article on spam prevention in exim mail servers. Think of it as an appendix. If you are starting from scratch you might find is useful to go and read that first. Read Ryan Cartwright's article in full at Freesoftware Magazine.

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