Where should the PTR of the mail domain look?

Question

Domain Name System

The answer, as it were, is obvious in itself, I decided to ask just in case
We always did ptr in hello domain.ru, while mx was set to mail.domain.ru
in the sender, we also have domain.ru
All ptr checks give the correct ip 0.0.0.0 .0 = domain.ru
Accidentally stumbled upon a tester that checks ptr in relation to MX
All the same, where should ptr look more correctly?

Answer 1

PTR must match HELO/EHLO, according to RFC 5321
o The domain name given in the EHLO command MUST be either a primary
host name (a domain name that resolves to an address RR) or, if
the host has no name, an address literal, as described in
Section 4.1.3 and discussed further in the EHLO discussion of
Section 4.1.4.
in EHLO the primary hostname (primary hostname) must be used.
Requiring a match with MX doesn't make sense, because many MXs can point to one server.
PS
in accordance with RFC 1035
- Gateways will often have two names in separate domains, only
one of which can be primary.
those. primary name can be one and by zone definition in-addr.arpa

Host addresses are represented by domain names that have all four labels
specified. Thus data for Internet address 10.2.0.52 is located at
domain name 52.0.2.10.IN-ADDR.ARPA. The reversal, though awkward to
read, allows zones to be delegated which are exactly one network of
address space. For example, 10.IN-ADDR.ARPA can be a zone containing
data for the ARPANET, while 26.IN-ADDR.ARPA can be a separate zone for
MILNET. Address nodes are used to hold pointers to primary host names
in the normal domain space.

those. both HELO and PTR also look at the primary host name, which hosts with names in many domains can only have one (even if they have multiple IP addresses).

Answer 2

ptr record is not DNS, but something the other way around, and is not at all like DNS records, in principle, the name may not match your domain, but so that letters do not fall into spam, the sending domain in the body of the letter must match what is stored ptr
Change ptr can only be the owner of the IP addresses you are given.
https://2whois.ru/?t=ptr - service for checking such records

Answer 3

PTR usually looks at the hostname of the server.