On Thu, Oct 09, 2003 at 09:07:42AM -0700, Richard Pitt wrote:
| One aspect of spam noted by a friend of mine in the computer security
| business is that many spam programs don't re-try if they get a soft
| error the first time.
|
| His initial thought was to introduce a cycle in the MTA that would
| reject all unknown sender/IP address combos the first time and allow
| them the second within a (relatively) short period of time (say 1 hour
| or 4 hours) since most spammers either don't retry at all, or retry the
| next "cycle" which may be many hours later if they are in the millions
| of addresses league.
|
| This aspect is due to the fact that the spam program doesn't run a
| "normal" MTA - one which retries as a rule and backs off on retry time
| to longer and longer times over a matter of days.
This is called greylisting and is available in many MTAs; Postfix v2
provides greylisting code in its sample policy daemon.
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