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