[Mimedefang] OT: DNS sanity check

[alan premselaar]

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I've been scouring thru RFCs trying to find specific information about
this to no avail.

sorry for the OT post, but the list traffic is sane enough and I suspect
there are plenty of qualified people here that I might actually get a
useful answer.

I have a situation where one of the ISPs i'm working with has started to
reject mail from my mail servers since we've moved into a new data center.

currently our mail server doesn't have a reverse DNS PTR record
configured and i'm in the process of getting that fixed.  In the
meantime I decided (based on bounced mail) to route outgoing mail via a
machine I have in the US which *does* have a reverse DNS PTR record for it.

the problem is, the reverse DNS PTR record for that machine is
mail.12inch.com (my domain) ... i've moved the mail server for this
domain to another machine in our datacenter here (which subsequently
doesn't have a reverse DNS PTR record yet) but have changed the forward
record for mail.12inch.com to reflect the IP address of this new machine.

the problem I'm told by the ISP is that they're rejecting mail from my
machines because:

a) machine #1 doesn't have a reverse DNS PTR record defined
b) machine #2 has a PTR record defined, but it doesn't match the forward
A record

I can *kind of* understand why they would reject a connection from a
machine with no PTR record, although since outgoing-only mail servers
are valid, they shouldn't necessarily require a PTR record, right?

what gets me is, is there actually any requirement that the A record and
the PTR record for a host match? i'm under the impression that they are
unreasonably rejecting mail but I just want to get a sanity check before
i start screaming at them (it's been a long day).

so, any information, assistance, references to RFCs, etc. would be
greatly appreciated.

Thanks.

Alan
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