Fixing "550 5.7.25" reverse DNS (PTR) rejections

550 5.7.25 is a reverse-DNS rejection. Reputable mail servers require the connecting IP to have a PTR record, and increasingly that it forward-confirms (FCrDNS): the hostname the PTR points to must resolve back to the same IP.

What it means

Reverse DNS maps an IP back to a hostname. No PTR — or a PTR whose hostname does not resolve back to the IP — reads as a careless or residential sender, so mail is refused before the message body is even sent.

Why it happens

The IP has no PTR at all, the PTR points to a generic hosting hostname with no matching forward record, or you are sending directly from a dynamic/residential IP that will never earn trust.

Diagnose it

The reverse-DNS tool below shows the PTR for the sending IP and whether it forward-confirms. If it is empty or mismatched, that is your fix.

Fix it

1. Ask whoever controls the IP (your host or ISP) to set a PTR to a real hostname you own, e.g. mail.example.com.

2. Publish a matching forward A record so PTR → hostname → IP round-trips and FCrDNS passes.

3. If you cannot control rDNS, send through a smarthost/relay that already has proper reverse DNS.