Forward and reverse should agree
Forward DNS (A or AAAA) says “this name is this IP.” Reverse DNS says “this IP is this name.” Many inbound mail filters check that the connecting IP has PTR, and that the PTR hostname has an A/AAAA back to the same IP. Hosting providers usually control in-addr.arpa and ip6.arpa, not your domain registrar — you request PTR through whoever assigned the address.
IPv4 reverses as dotted octets then .in-addr.arpa. IPv6 reverses nibble by nibble under .ip6.arpa. DNSFetch builds that name for you.