Reverse DNS Setup for an IP with multiple domains

Martin asked:

I am trying to clarify my Reverse DNS PTR lookup for a domain. I have a server with a single IP addresses and multiple accounts, all sharing that IP address;

My PTR is currently:

 24.210.31.in-addr.arpa. 14400 IN PTR domainname.co.uk.

But the domain that the IP address reverses to is ns1.domainnetwork.co.uk, therefore should the PTR record on the account reference the primary returned domain rather than the account domain?

I can’t seem to find any clear guidance on this with Google searching, however this question did seem to suggest that the account should reference the server domain rather than the account specific domain.

So, would having :

24.210.31.in-addr.arpa. 14400 IN PTR ns1.domainnetwork.co.uk.

in the DNS for the account give it a valid PTR record, even though this doesn’t mention the account domain at all?

Edit: To clarify, the ns1.domainnetwork.co.uk is the primary name server for the domain.

My answer:


Mail servers will cross-check your SMTP server’s advertised HELO hostname against the PTR record for the connecting IP address, and then check that the returned name has an address record matching the connecting IP address. If any of these checks fail, then your outgoing mail may be rejected or marked as spam.

So, you need to set all three consistently: The server’s hostname and the name in the PTR record must match, and that name must resolve to the same IP address.

Note that these do not have to be the same as the domain names for which you are sending mail, and it’s common that they are not.


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