PTR record (reverse DNS)

The record that maps an address back to a name, and the only one you cannot publish yourself. It lives in the in-addr.arpa tree, delegated to whoever owns the address range — your hosting provider — so it is set in their control panel, next to the server, not in the zone you edit at your registrar. Adding a PTR to example.com's zone does nothing whatsoever: dig +short -x 203.0.113.10 still answers with the provider's generic name. It matters most for mail. A receiving server checks that the name the PTR gives resolves back to the address talking to it, and a mismatch with the name you announce in HELO is enough to have the message filed as spam or refused outright, whatever your SPF, DKIM and DMARC say.