OT: Be sure your rDNS is in place...

[Bill Campbell]

On Mon, Jun 28, 2004, Fairlight wrote:
>At Mon, Jun 28, 2004 at 12:05:50AM -0400 or thereabouts, 
>suspect John Esak was observed uttering:
>> says they will do this in their contract, but they didn't! So for about two
>> and half years I've been running and periodically getting (but really very
>> rarely) email sent back because the reverse DNS was not there. I kind of
>
>If you've been doing that for 2.5 years and are first seeing results like
>that now, you've been very lucky indeed.  IgLou, for instance, has been
>doing that for years.  I think it's been at least two years since most
>vendors started shipping linux platforms with sendmail configured to reject
>on no rDNS.  I think exim always has been set that way, though that's a
>hazy memory.
>
>Suffice it to say, it's been going on for a long time and some places are
>now playing catch-up.
>
>Now what -has- gotten more stringent is that you used to be able to just
>have a PTR for your IP# that pointed to -any- valid hostname.  As long as
>it could be looked up, it was accepted.  I could set up a client site and
>make the PTR for an IP# point to any of their valid A record hostnames.
>Used to do that when masquerading.
>
>This is no longer the case.  In the last year, software and institutions
>have increasingly clamped down on that, and you have to match the A and PTR
>records or it goes *poof*.

Actually that will happen only if the mail administrator is severely clue-
deficient as many (most) virtual hosting servers send from IPs where the
hostname and rDNS don't match.  There will be entirely too many false
positives if one requires that they match.

What postfix does in its checking is to require (a) that the rDNS resolve
to some hostname, and (b) that there be an ``A'' record for the rDNS
resolved hostname.

We had a local person who is on DSL from a reasonably clued regional ISP
where there was no rDNS.  The problem wasn't his ISP, but the fact that the
ISP's upstream, uu.net, didn't delegate the DNS responsibility for the net
block to the regional ISP.

Bill
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