> AFAIK, no, that is wrong. The PTR for a MX should point to a > full name, including domain and host....
How do you expect that to happen in the real world where IP addresses are limited and ISPs use the same box with the same IP address for multiple services?
Almost all programs that look at reverse DNS entries for any reason will only look at the first one.
It's fine to have many A records pointing to the same IP, but having many PTR records for that IP doesn't do anything useful, and can cause problems.
According to the Bind Book it is allowable to have multiple PTR records to one IP address.
Yes. It is definitely allowed. However, it isn't used. For example, some anti-spam programs look at the reverse DNS entry for an IP: they just look at the first one that is returned. If you have multiple PTR records, you'll get a random one each time, which can cause sporadic issues.
-Scott
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