I am looking at PTR checking on a email server. In test, I see there are a few DNS setups where they CNAME their PTR records. From a RFC standpoint, is this valid, I am not finding any data to claim one way or the other.
If it is acceptable, and I realize this is getting as bit off topic, is the only recourse to simply whitelist those hosts that are doing this? Here is the first one I found, that tripped up my filter test (mysql mailing list): $dig -x 213.136.52.31 ; <<>> DiG 9.4.2-P2 <<>> -x 213.136.52.31 ;; global options: printcmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 28031 ;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;31.52.136.213.in-addr.arpa. IN PTR ;; ANSWER SECTION: 31.52.136.213.in-addr.arpa. 86400 IN CNAME 31.0-25.52.136.213.in- addr.arpa. 31.0-25.52.136.213.in-addr.arpa. 3600 IN PTR lists2.mysql.com. -- Scott
