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Article: 313
From: Erik Hensema
Date: 2005-01-25 05:29:52 -0500
Subject: Re: milter-ahead on a backup mx

Removal...........: milters-request@milter.info?subject=remove
More information..: http://www.milter.info/#Support
--------------------------------------------------------

On Tue, Jan 25, 2005 at 08:40:50AM +0100, Anthony Howe wrote:
[rejecting mail on backup mx when primary mx is online]
> I've been rereading RFC 974 MAIL ROUTING AND THE DOMAIN SYSTEM. In 
> particular section "Interpreting the List of MX RRs", paragraph 7, 
> sentence 2 and 3:
> 
> 	The mailer is required to attempt delivery to the lowest
> 	valued MX. Implementors are encouraged to write mailers so
> 	that they try the MXs in order until one of the MXs accepts
> 	the message, or all the MXs have been tried.
> 
> The only requirement above is a client MUST try the primary MXes
> first before trying secondary MXes. It does NOT say that they MUST only 
> delivery to the primary when it is online. The above suggestion might 
> break legit mail delivery in the event of temporary (421 busy signal) or 
> permanent rejection (554 weclome message) from the primary.

Good point. Maybe the milter should give a 4xx if and only if the primary
mx would accept the message. In all other cases, revert to the default
behaviour of milter-ahead.
-- 
Erik Hensema (erik@hensema.net)

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