HELO rejected error: Rejected because of the HELO/EHLO greeting
The server announced itself with a hostname the receiver won't accept - not a fully-qualified domain name, an IP literal or one that doesn't resolve.
How to fix HELO rejected
- Configure the mail server to greet with a real, resolvable hostname (mail.yourdomain.com), not 'localhost' or the bare IP.
- Make that hostname match the IP's reverse DNS.
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 HELO rejected 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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