[exim] Exim trying to send email to A record of recipient do…

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Autor: Konstantin Boyandin
Data:  
Para: exim-users
Asunto: [exim] Exim trying to send email to A record of recipient domain
Hello,

Exim version: 4.86, built from sources on Amazon OS.

Problem: I have noticed several cases (3, during last 2 months) when
mail log contains records like:

2016-02-08 14:22:25 1aSmfZ-0004Tg-UN ** user1@???
<user-list@???> R=dnslookup T=remote_smtp H=example.net
[10.1.2.3] X=TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256 CV=no: SMTP error
from remote mail server after RCPT TO:<user1@???>:
550-Verification failed for <user-list@???>\n550-No Such User
Here"\n550 Sender verify failed

The funny thing is Exim attempt to connect to A record address (in this
example, 10.1.2.3) of the target domain (example.net in this case),
whereas its MX records (10.10.1.2, 10.20.2.3, for the sake of example)
are valid, accessible and accept mail normally.

I tried to use /etc/hosts and add corresponding line, like

10.10.1.2 example.net

(the IP is the IP of MX record for the domain), but Exim ignores that
and still does actual DNS requests for A record and attempts to use it.

Can this Exim behavior be changed? At least, force Exim to consult
/etc/hosts in such a case, if DNS requests time out (the only cause of
this behavior that I can offer).

Thanks.

Sincerely,
Konstantin