How to create Mutiple PTR records for mail server?

Question

Domain Name System

We have a dozen sites on the server, each domain is delegated to Yandex DNS and uses PDD.
+ We have Exim on the server, which processes all letters from these sites.
Because Since it is possible to register only one PTR record, it was decided to beat this through Yandex DNS.
I came across recommendations:
Option 1.
IN MX 10 mail.mydistrict.k12.in.us
mail.mydistrict.k12.in.us. IN A 165.138.129.50
and for the ptr
50.129.138.165.in-addr.arpa. IN PTR mail.mydistrict.k12.in.us.
Then setup conical (cname) records for the pop3.mydistrict.k12.in.us and exchange.mydistrict.k12.in.us and not use A records for these.
Option 2:
www.example.com and www.yourdomain.example both resolve to 192.0.2.1.
The PTR for 192.0.2.1 is myhost1.yourdomain.example.
myhost1.yourdomain.example resolves to 192.0.2.1.
As I understood in the last version, we create a fictitious subdomain for the PTR and add records to the DNS for each domain. Question: is this correct and which type of record should I choose, CNAME or A?

Answer 1

Create a curly subdomain for host record type A, for PTR type PTR in the reverse zone. You yourself wrote everything in the question. Or I didn't understand what you didn't understand.
PS
Now I understand that you didn't understand -) I re-read the problem again.

Answer 2

For IP, for a number of reasons, having more than one PTR record is not recommended, although it is technically possible.
If you want to use your own hostname (and PTR) for each domain, allocate a separate IP and write a PTR for it.

Answer 3

No need to create multiple PTRs, one PTR is enough. The main thing is that the name contained in the PTR resolves back to the same address, and does not look like a dynamic one (does not contain a bunch of numbers, for example), ideally it contains the word mx or mail and it is desirable that the PTR matches the domain that your server uses in HELO/EHLO.