About reverse DNS
Reverse DNS maps an IP address to a domain name using a PTR (pointer) record stored in a special DNS zone (in-addr.arpa for IPv4, ip6.arpa for IPv6). This is set by the IP block owner - typically your ISP or hosting provider - not by the domain owner. A missing PTR record can cause email servers to classify your outbound mail as suspicious, since many anti-spam systems verify that the sending IP resolves to a hostname. For mail servers, the PTR hostname should ideally forward-confirm back to the same IP.