[Exim] 'Unrouteable mail domain'/sporadic MX lookup failures

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Autor: Adam Newby
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A: exim-users
Assumpte: [Exim] 'Unrouteable mail domain'/sporadic MX lookup failures
We've been experiencing a problem whereby MX records fail to be found for
some domains when exim does a DNS lookup (NB as distinct from timing out
when trying to do the MX lookup). In this case, exim appears to
bounce the message immediately. This appears to be an intermittent
problem, as the MX lookup is found OK with emails at other times.

Can anyone shed any light on this problem:

1. Could this be a problem with our local BIND installation? We run 8.3.x
rather than 9.x.

2. Can exim be made to retry in the event of no MX records being found?
Looking at the source code, I'm not sure if this is possible without a
code change, but I may be wrong.

Also, exim's behaviour in bouncing such messages immediately seems
inconsistent. If it fails to find an MX record, it looks for an A record
instead (for some reason!). For many people, this points at a machine not
running a mail server, and often with a firewall, so exim attempts to
contact it, and times out, causing the message to be deferred for retry
later. If it happens that there's no A record, the message bounces.


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