Mail transport & reputation

What is Reverse DNS (PTR)? Reverse lookup of an IP address explained

Reverse DNS maps an IP address to a host name (PTR record). Mail servers without matching reverse DNS end up in spam or are rejected by many receivers.

How Reverse DNS (PTR) works

The PTR record does not live in your domain's zone but in the reverse zone of the IP address (in-addr.arpa for IPv4, ip6.arpa for IPv6). Only the owner of the IP address can set it – usually your hosting or server provider.

Receiving servers often check forward-confirmed reverse DNS: the IP points to a host name via PTR, and that host name points back to the same IP via an A or AAAA record. Google requires valid forward and reverse DNS for sending servers.

The Domain Trust Check checks the reverse DNS of the mail servers listed in the MX records. Often the same servers also send the outgoing mail.

Example

; IP 203.0.113.25 belongs to mail.example.com
25.113.0.203.in-addr.arpa.  PTR  mail.example.com.
mail.example.com.           A    203.0.113.25

PTR and A record point to each other – the normal case for a properly configured mail server.

Common mistakes

No PTR record, or a generic name such as "static-203-0-113-25.provider.net".
The PTR points to a host name that does not resolve back to the same IP.
The record was looked for in your own DNS zone instead of being requested from the IP provider.

How the Domain Trust Check rates Reverse DNS (PTR)

Criterion “MX configuration” (weight 5 of 5): MX records present or null MX (RFC 7505), all MX hosts resolvable, no CNAME, public IP addresses, matching reverse DNS (PTR), redundancy and IPv6.

Standard: RFC 1035, RFC 1912