I am dealing with a correspondent whose "ultimate" sending mail server's PTR
record contains a non-existent host. This is preventing delivery to gmail.
In this case (headers from a message received elsewhere):
--
Authentication-Results: mx6.messagingengine.com;
[...]
iprev=fail smtp.remote-ip=23.24.6.165
(Error NOERROR looking up 23.24.6.165 PTR,Error Error NXDOMAIN looking up
23-24-6-165-static.hfc.comcastbusiness.net. A looking up
23-24-6-165-static.hfc.comcastbusiness.net. A,Error Error NXDOMAIN looking up
23-24-6-165-static.hfc.comcastbusiness.net. AAAA looking up
23-24-6-165-static.hfc.comcastbusiness.net. AAAA);
[...]
Received: from atlas.bondproducts.com (unknown [23.24.6.165])
by mx6.messagingengine.com (Postfix) with ESMTP id ...
[...]
Received: from users.shellworld.net (users.shellworld.net [50.116.47.71])
by atlas.bondproducts.com (Postfix) with ESMTP id ...
--
I am curious about the exact mechanism of PTR checks, and couldn't find it in
RFC5321 so presume it's not actually part of SMTP.
Does anyone know if/where this is specified, or is it up to providers to do
their own thing?
It seems it should be possible to have multiple DNS records of various sorts
for the same IP as long as the IP of the host in PTR matches the IP of the
ultimate sending server, or that's my interpretation of the NXDOMAINs above and:
https://serverfault.com/a/193820
...but would like to read it from the horse's mouth.
Thanks,
Gareth
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