Fighting spam via greylisting
bish at airtelbroadband.in
Wed Apr 25 08:13:33 PDT 2007
On Wed, Apr 25, 2007 at 12:04:19PM +0300, Ag. D. Hatzimanikas wrote:
[ some snipped ]
> The logic behind greylisting is rejecting email with a
> temporary error code -- which is defined in RFC 821  and
> should be honored by the moderns MTA's-- so:
> - Any "well behaved"  MTA will try to resend the
> email, which is exactly what we want.
> But the 450 code is described as: User not active now.
> Isn't this (when with our software return 450) some
> kind of a violation? Personally I would like an answer
> about that, because quite possible, as a novice in
> these matters, I'm missing something.
> - The spam software will see the error code (450)
> and quite possible will not try to resend the email,
> considering as a dead connection.
[ more snipped ]
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.
Would this explain the missing link ?
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