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-----Original Message-----
From: Uncle George [mailto:netbeans@gatworks.com]
Sent: Monday, November 27, 2006 3:07 PM
To: Jason Frisvold
Cc: qmail@list.cr.yp.to
Subject: Re: Advanced tricks I use to get rid of spam using MX 4xx
Jason Frisvold wrote:
> On 11/27/06, Marc Perkel <marc@perkel.com> wrote:
>
>> No - on my system a 4xx error only means that that particular server
>> isn't
>> ready. It means try the other servers or come back later. It
>> certianly dos
>> not mean that all the servers aren't ready. That's what I use EXIM
>> and not
>> Qmail. All other MTAs except Qmail behave this way. it's what the
>> spec says.
>> Qmail does it wrong.
>
>
> Hrm.. I find this interesting and slightly disturbing. Can you
> please provide the spec and highlight the passage which identifies
> this behavior as correct?
>
> I'm not sure I like the idea of a mail server immediately trying
> another MX if the initial one it contacted was busy. This just
> creates additional load on the other MXs and can cause additional
> meltdown. I believe the "correct" way for this to work is to queue
> the message when a 4XX is received and retry later. When later
> arrives, the MX lookup is repeated and at that point it's possible
> that an alternative server is chosen.
>
I thought this was relevant, and should have answered your question:
> as per section 5 of RFC 2821 circa 2001: Address Resolution and Mail
> Handling
>
> To provide reliable
> mail transmission, the SMTP client MUST be able to try (and retry)
> each of the relevant addresses in this list in order, until a
> delivery attempt succeeds. However, there MAY also be a configurable
> limit on the number of alternate addresses that can be tried. In any
> case, the SMTP client SHOULD try at least two addresses.
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