Reverse DNS is a way of associating an IP address with its domain name.
The reverse DNS identifier is contained in the PTR portion of the IP Zone File.
The IP Zone File contains all the different ways that your IP and domain name can be associated; each association serves a different need.
- If the sender's domain is the only domain sending mail from a specific IP address, we recommend that the reverse DNS entry (PTR Record) match the domain name (A Record), but we do not require it.
- AOL does require that all connecting Mail Transfer Agents have established reverse DNS, regardless of whether it matches the domain.
- Reverse DNS must be in the form of a fully-qualified domain name - reverse DNSes containing in-addr.arpa are not acceptable, as these are merely placeholders for a valid PTR record. Reverse DNSes consisting only of IP addresses are also not acceptable, as they do not correctly establish the relationship between domain and IP address.