SMTP codes
SMTP 5.7.25 Reverse DNS validation failed
Your IP has no PTR record, or the PTR does not resolve back to the IP. Gmail and many others require it.
- Class
- 5xx · Permanent failure
- Retried?
- No, the message bounces
- Defined in
- RFC 7372 / provider
What to do
- Ask your hosting or ISP to set PTR to your mail host name (mail.example.com), and an A record back.
How it appears in a bounce
550 5.7.25 Reverse DNS validation failed
Paste the full bounce into the decoder — it finds every code and recipient and says what to check.