Fighting spam via greylisting
Felix M. Palmen
zirias at despammed.com
Wed Apr 25 12:08:48 PDT 2007
* USM Bish <bish at airtelbroadband.in> [20070425 20:43]:
> IIRC, usually greylisting involves sending Err Code 451 (viz
> Requested action aborted: local error in processing). Since
> this implies that ATRN request cannot be processed now, or a
> temporary failure, most modern MTAs resend the mail on receipt
> of Err 451.
> OTOH, Err Code 450 is "Request mail action not taken: mailbox
> unavailable" (which is perhaps what you mean by saying "user
> not active now"). This is a serious error, and indicates ATRN
> request has been *refused*. MTAs compliant with RFC 822,
> should not respond this.
That's wrong. Every 4xx code is considered a temporary error, and
sending MTAs /should/ retry, but they are not required to do so.
Only the 5xx codes are used for permanent errors and indicate that the
sender must not retry the same transaction.
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