On the Wed, Mar 26, 2008 at 02:42:36PM +0100, Tonnerre Lombard blubbered:

Hoi.

> 1. it is highly unlikely that these stupid wannabe SPAM filters get the
>    response containing so many PTR records right. It is most likely
>    that either the software blows up or that it only ever considers the
>    entry it receives first.

Most mailservers just check if there is a PTR record at all and
if there is none, reject the mail with a 5xx DSN.

>    (Most likely the software blowing up will not even be remarked but
>    instead the mail will be rejected silently.)

Clever spamfilters will just add another score point to the spam
score and not just pass or discard a mail based on a single
criteria. 

> > Under the line, it is likely not a DNS issue, but the inability by
> > some mail or AS systems resolving lists. Suspect my servers will
> > fail, too. Xaver, pls send private reply for a test from that system,
> > anytime.
> 
> It is also a DNS issue, depending on the number of results returned;
> the size of a DNS/UDP response is limited to 1 UDP packet, which again
> is limited in size. Not everyone uses DNS over TCP, and it is unlikely
> to be adapted just because of such a stupid and useless SPAM filtering
> measure.

While Xari's Setup with tons of PTR records is plain stupid.
Xari, you should have a read about MX records. =:-)

But DNS uses UDP and TCP as I just checked. RFC 1035, Chapter 4.2 says:
"The Internet supports name server access using TCP [RFC-793] on
server port 53 (decimal) as well as datagram access using UDP [RFC-768]
on UDP port 53 (decimal)."

CU, Venty

-- 
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