Script get all MX record for domain and check them PTR record. And you can use another DNS server in 2th parameter of script

Example:

vint@postfix:~$ ./check_domain.sh telegram.org

Checking domain: telegram.org
The DNS server used is: 127.0.0.53

Resolved DNS names in:
        149.154.167.99
Looking for MX records
        mx10.telegram.org.
                95.161.64.10 ... check PTR record ... OK
        mx101.telegram.org.
                95.161.64.16 ... check PTR record ... OK
        mail.telegram.supply.
                95.161.64.2 ... check PTR record ...PTR record not found

or with another DNS server

vint@postfix:~$ ./check_domain.sh telegram.org 8.8.8.8

Checking domain: telegram.org
The DNS server used is: 8.8.8.8

Resolved DNS names in:
        149.154.167.99
Looking for MX records
        mx101.telegram.org.
                95.161.64.16 ... check PTR record ... OK
        mx10.telegram.org.
                95.161.64.10 ... check PTR record ... OK
        mail.telegram.supply.
                95.161.64.2 ... check PTR record ...PTR record not found

Warning, this script fails for MXs associated with major mail services like Google etc. But Postfix does not throw an error for these mail servers.