contact - SMTP-side domaincheck checks IPv4 only, rejects domains with first MX on IPv6

Jeroen Massar jeroen at
Sun Jun 5 13:22:21 UTC 2011

As the subject states,


<.... at>:
Connected to 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 [email protected] thus no way to
tell them through that route.


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