I thought that it only had to exist.
That's better than nothing and already distinguishes the IP of your outbound MTA from all the IPs that have no PTR.
In our case (and in many cases as I talk with more admins) the reverse DNS for our static Ips is not delegated by our ISP, but returns their name in the reverse DNS lookup. I have been told repeatedly that this is OK, as long as something is returned.
Can someone clarify?
The "best practice" for an outbound MTA is for its PTR hostname to have a "matching" A record, in the sense that the query for the A record of the PTR hostname returns the IP of the MTA.
example:
;; ANSWER SECTION: 75.210.73.212.in-addr.arpa. PTR mgw1.meiway.com
;; ANSWER SECTION: mgw1.meiway.com. A 212.73.210.75
The other best practice is to have only one PTR record per IP. Since all widely used applications use only one (the first) PTR record, returning only one PTR is the only way to assure the querier receives a specific PTR and not an indeterminate "first" PTR of multiple PTRs.
Len
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