messagelabs.com contact - SMTP-side domaincheck checks IPv4 only, rejects domains with first MX on IPv6
As the subject states, MAILER-DAEMON@messagelabs.com: <....@ford.com>: Connected to 136.1.7.8 but sender was rejected. Remote host said: 501 Sender domain must exist As it obviously checks only the first MX record if there are A records, and if there are none it rejects it. This while there are AAAA records on the first MX, and even A records on the remaining MXs. Thus a proper fix would already be to check the other MXs and of course to check for AAAA too ;) And that affects all customers at messagelabs, thus if somebody can pass that along to them to fix it, that would be great ;) Oh and of course the check is also there for postmaster@ thus no way to tell them through that route. Greets, Jeroen
I'll get someone to contact Ford and see what they are running. From google it looks like Exchange. Is this a known bug with Exchange? If so I think there's bigger problems than messagelabs :) Jeroen Massar wrote:
As the subject states,
MAILER-DAEMON@messagelabs.com:
<....@ford.com>: Connected to 136.1.7.8 but sender was rejected. Remote host said: 501 Sender domain must exist
As it obviously checks only the first MX record if there are A records, and if there are none it rejects it. This while there are AAAA records on the first MX, and even A records on the remaining MXs. Thus a proper fix would already be to check the other MXs and of course to check for AAAA too ;)
And that affects all customers at messagelabs, thus if somebody can pass that along to them to fix it, that would be great ;)
Oh and of course the check is also there for postmaster@ thus no way to tell them through that route.
Greets, Jeroen
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On 2011-Jun-06 00:07, Matt Sergeant wrote:
I'll get someone to contact Ford and see what they are running. From google it looks like Exchange. Is this a known bug with Exchange? If so I think there's bigger problems than messagelabs :)
Ah good catch, indeed the messagelabs.com SMTP is not the blame here, it forwards it internally to a ford.com one which rejects it. One of the mail servers that is broken in that respect upto a very recent version is Communigate Pro. As for the backscatter that the above setup can generate, you might want to implement the same checks on the front-ends, or at least ask the customers you are forwarding to to disable these checks at least for your frontend servers as now as you can see, the messagelabs.com smtp accepted the email and then started rejecting it. If somebody thus nicely 'forges' (well just fills in a random) email address, the ford.com server will reject it, and messagelabs starts spamming them with the full message which is included in the bounce.... Oh, gee, now lets hope spammers don't abuse that 'feature' eh... Greets, Jeroen
participants (2)
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Jeroen Massar -
Matt Sergeant