[Exim] Exim 4.22 Delivering to Itself Instead of Queuing

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Author: David Kreindler
Date:  
To: exim-users
Subject: [Exim] Exim 4.22 Delivering to Itself Instead of Queuing
In DNS, we have entries like:

    @ IN MX  0 mail
      IN MX 10 mx1
      IN MX 10 mx2


When mx1 or mx2 receive a message that cannot be relayed to 'mail', they deliver to themselves and to each other instead, eventually resulting in a 'Too many "Received" headers - suspected mail loop' error. The Exim main log shows "R=dnslookup" with deliveries not only between mx1 and mx2 but also between mx1 and itself and between mx2 and itself.

My understanding is that a MTA should never deliver to itself or an equal-preference MX. So when 'mail' is not available, mx1 and mx2 should simply queue the message. Instead, they deliver to each other and to themselves.

The routers config has:

    dnslookup:
      driver = dnslookup
      domains = ! +local_domains
      transport = remote_smtp
      ignore_target_hosts = 0.0.0.0 : 127.0.0.0/8
      no_more


The 'local_domains' lists have @, @[] and every name by which the local host might be known.

What might be causing this strange looping behavior?