Reverse DNS (PTR)

Most reputable mail servers reject mail from any IP that has no PTR record, or whose PTR looks like a dynamic consumer IP (e.g. `c-73-xx-xx-xx.hsd1.ca.comcast.net`). You need to ask your hosting provider or ISP to set a proper PTR pointing at your mail domain.

Only the owner of the IP block can set PTR records. If you own the IP (leased a /24 or bigger from an RIR), yes. Otherwise, open a ticket with your hosting provider.

Best practice: yes. The PTR should resolve to a hostname whose A record points back to the same IP. This is called FCrDNS (Forward-confirmed reverse DNS) and is required by many anti-spam systems.