>># host mail.example.com
>>mail.example.com is an alias for hostname.example.com.
>>hostname.example.com has address

>Wrong. The MX record has to point to an A name, not a CNAME.


MX record's data field is a domain name

That domain name owns one or more A records.

With mail, the shortest resolution path is always best practice, and resolving through a CNAME is not the shortest.

Similarly, an MX's IP should have only one PTR record, whose domain name in the data field "matches" with an A record:

d.c.b.a.in-addr.arpa. PTR label.domain.tld.

label.domain.tld. A a.b.c.d


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