Typically when setting up a mail server, I create an rDNS record for the mail server IP to match the mail server hostname (ex: mail.example.com).

Can I instead set the rDNS ptr to match the parent domain (e.g. example.com), if this server is being used for multiple purposes, and still send mail successfully (i.e. not be classified as spam b/c of mismatched rDNS)?


EDIT: The article at http://en.wikipedia.org/wiki/Forward_Confirmed_reverse_DNS seems to indicate that it might be more complicated than I had thought. For instance, 1) I did not know that you could have multiple PTR records for a given IP; 2) it appears that as long as each PTR record matches an A record, everything is good (basically nullifying my question). Would you agree?


Most receiving mail servers that I have encountered in the wild look to make sure that the incoming IP address has a reverse DNS entry and stop there. For the most part, as long as one exists, it will be accepted.

Some will try to resolve the hostname returned from the reverse DNS lookup and ensure it resolves (but it need not match the incoming IP). Some go as far as to compare the results (hostname must match the incoming IP).

I generally ensure a "resolution loop" by having the hostname map to the IP, and the reverse entry on the IP match the hostname. Just having a reverse DNS entry will be sufficient in most cases, even if it doesn't match perfectly.

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