What is / Full version

PTR records for mail

Reverse DNS maps client IPs to names. Some receivers compare those names to EHLO hostnames.

Forward-confirmed reverse DNS

Operational mail best practice is that the EHLO name resolves forward to the client IP and the client IP's PTR resolves back to that same name. Gmail's SMTP error list quotes failures when that relationship breaks.

Not authentication

PTR does not replace SPF, DKIM, or DMARC. It is a hygiene signal. A correct PTR without SPF pass does not authorize a sender.

Delegation

The IP network operator or cloud provider usually publishes PTR for addresses it assigns. The domain's SPF and DMARC TXT records are published in the domain zone, which is a different administrative step.

A VPS that sends mail needs PTR from the hoster and SPF from the domain owner. Missing either can trigger different rejection reasons on large receivers.

Operational practice

Operators publish PTR for sending IPs and ensure forward DNS for the EHLO name resolves back to the same address. Gmail's SMTP error list quotes several rows where that relationship fails.

PTR is not a substitute for SPF. A message can present a matching PTR and still fail SPF if the IP is not authorized in the SPF record.

IPv6 PTR uses ip6.arpa delegation. The same EHLO and PTR consistency checks apply when receivers quote IPv6-specific SMTP errors.