better blocking at MTA level (off-topic)

[Andrew MacLachlan]

Mailcontrol treats all 45x responses as 550 - although they should know better...

----- Original Message ----
From: Jason Ede <j.ede at birchenallhowden.co.uk>
To: MailScanner discussion <mailscanner at lists.mailscanner.info>
Sent: Saturday, 26 May, 2007 6:17:23 PM
Subject: RE: better blocking at MTA level (off-topic)

> -----Original Message-----
> From: mailscanner-bounces at lists.mailscanner.info [mailto:mailscanner-
> bounces at lists.mailscanner.info] On Behalf Of Dhawal Doshy
> Sent: 26 May 2007 12:34
> To: MailScanner discussion
> Subject: Re: better blocking at MTA level (off-topic)
> 
> Jason Ede wrote:
> > The problem with greylisting as we found when we enabled it was that
> > some MTA's treat a temporary reject code (450) as a permanent reject
> > code (550) and our customer was complaining that they weren't
getting
> > email. Whilst we could exempt every MTA they flag up to us from
> > greylisting checking there is no way to prevent email from an
unknown
> > source getting blocked and not getting through to them. Until we can
> > resolve the problem without telling our customer to tell anyone
> emailing
> > them with problems to get their MTA fixed it unfortunately has to be
> > off... It did vastly reduce the load on our server whilst
greylisting
> > was active though.
> 
> Change 450 to 451 to reduce false positives.. exchange responds better
> to a 451 (as compared to 450). See
> ftp://ftp.rfc-editor.org/in-notes/rfc2821.txt
> 
>        450 Requested mail action not taken: mailbox unavailable
>           (e.g., mailbox busy)
>        451 Requested action aborted: error in processing

Wouldn't 451 responses cause more problems with some MTA's just
returning the mail to sender? Or is it just exchange that tends to
return 450's immediately?

Jason

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