Re: [exim] Outbound SMTP interface selection vs SMTP connect…

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Author: Dean Brooks
Date:  
To: Paul Warren via Exim-users
Subject: Re: [exim] Outbound SMTP interface selection vs SMTP connection re-use
On Fri, Nov 19, 2021 at 06:28:44PM +0000, Paul Warren via Exim-users wrote:
> We have an SMTP transport which selects the outbound interface based
> on a number of factors.
>
> We have noticed that if a mail is not delivered immediately, it is
> sometimes delivered as an additional message on an existing
> connection which may not be using the same interface.? In this case,
> the logs show it being delivered as the result of an "exim -MC"
> command.
>
> Is this expected behaviour, and is there anyway to control it so
> that the interface selection is always honoured for a message?


This problem was reported many years ago, per bug report tracker
https://bugs.exim.org/show_bug.cgi?id=1141

I believe a workaround was to use "connection_max_messages=1" on the
transport to allow only a single message on any given connection. We
made a special transport for the hosts that needed this so the rest of
our mail wasn't affected. Not sure if this is needed now, it's been a
while since I worked with interface switching.

-Dean