I have a customer who swears we have our reverse DNS set up wrong.....at dnsstuff.com we pass every test...except the
DNS timing test. If you put our customers domain (aclc.org) into the box and select PTR it says our DNS server reports
no PTR records (even though it is authoritive for our subnets).
A reverse DNS entry takes an IP address and converts it into a hostname. It does *not* take a hostname and convert it into a hostname (a CNAME record does that).
A mailserver that gets a connection from your mailserver doesn't care that you are aclc.org -- you could just as easily say you are microsoft.com. They care that you say that you are 192.0.2.25 (or whatever your IP is). So to find out if your mailserver has a reverse DNS entry, you have to find its IP, and check the reverse DNS entry for that.
Many domains I put in this test fail (even very well known ones).
As they should -- almost no domains have PTR records (a few do, probably because they didn't know what they were doing). :)
For the DNS timing test, you would need to enter the correct hostname for the PTR record (something like 25.2.0.192.in-addr.arpa). I'm going to add a note to the reverse DNS lookup tool to let people who enter a hostname know that it had to be converted to an IP, which may not be the IP that they were planning to look up.
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