550 5.7.25 error (Gmail): The sending IP has no valid reverse DNS
The IP that connected to Gmail has no PTR record, or the PTR's hostname doesn't resolve back to that same IP. Gmail requires a matching forward and reverse pair.
How to fix 550 5.7.25
- Ask whoever owns the IP (your host or ESP) to set a PTR record pointing to a hostname you control.
- Make that hostname's A record point back to the same IP, and use it as the SMTP HELO name.
Why this happens
Something in the server or DNS setup doesn't meet the basic rules of the SMTP conversation: how the server identifies itself, whether it has reverse DNS, whether it uses TLS, or whether it is allowed to relay at all.
How to keep it from coming back
Set a real hostname with matching forward and reverse DNS, enable TLS, authenticate before relaying, and re-test the setup after any change to your mail server or provider.
Should I retry a 550 5.7.25 error?
Not as it stands. A permanent error means the same message will be refused again until the cause is fixed on your side. Fix the cause first, then send a fresh message; if it keeps failing after that, check the full text of the bounce for the exact reason.
Got the full bounce message?
The text after the code names the exact reason, and the same code can mean different things at different receivers. Paste the whole message into the decoder - it runs in your browser and nothing is sent.
Open the bounce decoderRelated error codes
Seeing this again and again? That's usually a reputation or authentication problem we can trace and fix at the source.
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