Subject: greylisting (was: Re: Test (sorry))
To: Colin J. Raven <colin@kozy-kabin.nl>
From: Mirko Thiesen <thiesi@NetWorkXXIII.de>
List: netbsd-help
Date: 11/30/2004 10:18:03
On Tue, 30 Nov 2004, Colin J. Raven wrote:
> Sorry about this, it's a test to send some list traffic to my box.
>
> My mail server is suddenly bouncing mail from this list, and the list
> has also abrubtly stopped accepting mail from my server claiming a
> greylisting issue. Weirder still during the past 24 hours (when this
> first started happening) I haven't done anything to the box....anything!
>
> Oddly the mail logs stated something to the effect that my message had
> been rejected because it had been greylisted for 300 seconds...and to
> "try again later". That's sort of illogical somehow. You're either
> rejected or else you 'aint (so to speak).
Although I do not know why you are unable to receive mail from this list,
what you describe is exactly what greylisting does. The purpose is to
reject an incoming mail _temporarily_. Most spam bots will not bother to
retry sending the message and simply move on to the next victim whenever
they encounter any kind of failure. Your MTA should be able to distinguish
between a hard bounce (5xx) and a soft bounce (4xx), which is what
greylisting leads to. A hard bounce usually indicates a permanent failure,
so the sending MTA should not attempt any further deliveries, whereas a
soft bounce indicates that the reasons for not accepting the mail are of a
temporal manner. Thus, your MTA should try to deliver your mail again
after a defined period of time. Having put "you" into a database, the
receiving MTA knows "you" when your MTA eventually commences another
delivery attempt - if the time span between your retries lasts for at
least what the receiving MTA forces as a limit between deliviery attempts.
This is to prevent circumvention of the greylisting system by simply
hammering the receiving MTA with subsequent delivery attempts.
To put it short: You should not have to take any special actions in order
to send mail to the list. The fact that your message was distributed by
the list showes this, by the way. ;-)
Bye, K&K,
T-Zee
--
thiesi@NetWork23.Sytes.NET ---- NetBSD: Power to the people!
Tel.: ++49-(0)171-416 05 09 -- Fax: ++49-(0)171-134 16 05 09
Mirko Thiesen, Soemmeringstrasse 41, D-10589 Berlin, Germany
"We're with you all the way, mostly"