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This is the email header of one of our notification mails send through SMTP:

Received: from mgi74201.gutt.it (mgi74201.gutt.it. [5.9.63.186]) by mx.google.com with ESMTP id ABCD1234; Wed, 08 Aug 2012 09:36:18 -0700 (PDT) Received: from mgi74201.gutt.it (unknown [5.9.63.186]) (Authenticated sender: noreply@maxrev.de) by mgi74201.gutt.it (Postfix) with ESMTPA id ABCD1234 for <*@gmail.com>; Wed, 8 Aug 2012 18:35:55 +0200 (CEST)

As you can see google was able to check PTR:5.9.63.186 (resulting mgi74201.gutt.it.), but our own mail client results "unknown".

We've tested nslookup 5.9.63.186 and it results as expected:

Using username "abc". Authenticating with public key "abc" Last login: Wed Aug 8 19:31:01 2012 from 123.abc root@mgi74201:~# nslookup 5.9.63.186 Server: 8.8.4.4 Address:
8.8.4.4#53 Non-authoritative answer: 186.63.9.5.in-addr.arpa name = mgi74201.gutt.it. Authoritative answers can be found from: abc@mgi74201:~#

So why does the Reverse DNS not work? A postfix related problem?

EDIT: postfix results:

Aug 9 17:00:59 mgi74201 postfix/smtpd[19261]: warning: 5.9.63.186: address not listed for hostname mgi74201.gutt.it Aug 9 17:00:59 mgi74201 postfix/smtpd[19261]: connect from unknown[5.9.63.186]

But hosts file seems to be correct:

# 'hosts' file configuration. 

::ffff:5.9.63.186     mgi74201.gutt.it     mgi74201 
::1     ip6-localhost     ip6-loopback 
fe00::0     ip6-localnet 
ff00::0     ip6-mcastprefix 
ff02::1     ip6-allnodes 
ff02::2     ip6-allrouters 
ff02::3     ip6-allhosts 
127.0.0.1 localhost.localdomain localhost mgi74201.gutt.it.local 
# Auto-generated hostname. Please do not remove this comment. 
5.9.63.186 mgi74201.gutt.it  mgi74201
mgutt
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1 Answers1

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Try moving the last line of your hosts file into first position. The effect should be that mgi74201.gutt.it will get resolved to 5.9.63.186 instead of ::ffff:5.9.63.186

Or, maybe better, assign a different hostname to the IPv6 address, just like ip6-localhost differs from localhost.

Daniel Vérité
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  • Yes you are right. The problem was IPv6. Because the hosts file is generated automatically through the Control panel and can't be edited, we decided to deactivate IPv6 temporarily until we find a better solution. – mgutt Aug 12 '12 at 17:24