The PTR record, also known as a pointer record, has a very precise goal. It has to point the IP address to the domain name. In addition, this type of DNS record is able to work either with IPv4 addresses or with IPv6 addresses efficiently. Therefore, thanks to the pointer record, you are able to configure and perform Reverse DNS.
This DNS record gives the ability to ensure and verify that the particular IP address is exactly belonging to the domain name. That is very important when it comes to sending an email. The receiving mail servers usually desire to verify the source of the email and perform a reverse DNS lookup. Therefore, they examine and seek exactly the PTR records.