How to set primary domain for IP?

Question

Apache HTTP Server

Hello, it turned out that helo records in sent messages, mail services may not read in the body of the letter, but request by ip, respectively, the first domain name that hangs on ip always gets (if you have several sites on it)
How can I configure main domain name when requesting a name by ip?
Configuration:
Debian8
Bind9
Exim4.48

Answer 1

Something strange you ask. If we are talking about a PTR request (which is often done by mailers to check the validity of the server), then it is configured by the provider, this entry for one IP address is usually the provider alone (although DNS does not prohibit). It must match the name of the server who is the MX for the domain and is hidden behind the corresponding A record. Those. Roughly speaking, for a domain, there must be MX records leading to A records, which are supported by PTR records.
If you're talking about something else, please explain.

Answer 2

https://debian.pro/1977