Delivering mail to Comcast?

[Shane Kerr]

Hello,

I have been running my own e-mail server for many years now, and have
been native IPv6 for... maybe 5 or 6 years?

I never have any problems, except for delivering to Comcast users. I
get bounces like this:

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

  xxx at comcast.net
    SMTP error from remote mail server after initial connection:
    host mx2.comcast.net [2001:558:fe21:2a::6]: 554 resimta-ch2-08v.sys.comcast.net comcast ESMTP server not available
  yyy at comcast.net
    SMTP error from remote mail server after initial connection:
    host mx2.comcast.net [2001:558:fe21:2a::6]: 554 resimta-ch2-08v.sys.comcast.net comcast ESMTP server not available

Googling a bit I see this:

http://postmaster.comcast.net/smtp-error-codes.php

	Comcast requires all sending mail server IP addresses have a
	valid PTR record set up. This error results when the lookup failed.

	NXDOMAIN response. One of the authoritative servers for the
	relevant section of the in-addr.arpa DNS tree is saying that
	there is no PTR record for the given IP address. 

But I do have working reverse DNS:

$ ip addr | grep inet6
    inet6 ::1/128 scope host 
    inet6 2a02:2770::21a:4aff:fea3:eeaa/64 scope global dynamic 
    inet6 fe80::21a:4aff:fea3:eeaa/64 scope link 

$ host 2a02:2770::21a:4aff:fea3:eeaa
a.a.e.e.3.a.e.f.f.f.a.4.a.1.2.0.0.0.0.0.0.0.0.0.0.7.7.2.2.0.a.2.ip6.arpa domain name pointer c.time-travellers.nl.eu.org.

$ host c.time-travellers.nl.eu.org
c.time-travellers.nl.eu.org has address 46.19.37.141
c.time-travellers.nl.eu.org has IPv6 address 2a02:2770::21a:4aff:fea3:eeaa

The forward and reverse IPv6 DNS even match!

Are there any recommendations?

I hate to do AAAA filtering of Comcast's SMTP servers, but if that's
the only way to work around the brokenness, I guess I will so I can
talk to my family about their vacation photos... (Note that Comcast has
no issues sending me mail, so I get a lot of vacation photos.)

Cheers,

--
Shane
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 163 bytes
Desc: OpenPGP digital signature
URL: <https://lists.cluenet.de/pipermail/ipv6-ops/attachments/20161101/4df4508a/attachment.sig>