What it looks like in your logs
550 5.7.0 Mail relay denied [203.0.113.10]. Invalid credentials for relay for one of the domains in: example.com - gsmtpWhat does 5.7.0 mean?
RFC 3463 defines X.7.0 as other or undefined security status. The receiving server refused your message for a security or policy reason and chose not to use a more specific sub-code. On its own, 5.7.0 tells you only which family the problem belongs to. Your server will not retry it. The words that follow the code, and the three-digit reply in front of it, are what tell you where to look.
Gmail uses 5.7.0 for a surprisingly wide range of refusals: relay denied because the domain is not registered with the SMTP relay service, an account suspended for abuse, authentication or STARTTLS required before the command, and content flagged as a security risk. These have little in common, so matching on the code alone will send you in the wrong direction.
The basic reply code narrows it a little. With Gmail, 530 5.7.0 is usually a demand to authenticate or start TLS, 552 5.7.0 is about the message content, and 550 5.7.0 is usually about relay settings or the sending account. Beyond that, the words in the reply are the only real diagnosis.
Soft or hard bounce?
| Soft bounce (4xx) | Hard bounce (5xx) | |
|---|---|---|
| Nature | Temporary | Permanent |
| Sender behaviour | Queue and retry with backoff | Stop, suppress the address |
| Reputation risk | Low, unless it repeats for days | High above a 2% bounce rate |
| 5.7.0 | ✓ this code |
Common causes
- Relay was denied because credentials are wrong or the domain is not registered with the relay service.
- The sending account was suspended for abuse or a security issue.
- The server required authentication or STARTTLS before accepting the command.
- The message content, attachment or link was judged a security risk.
- The authenticated user tried to send as an address it is not allowed to use.
How to fix 5.7.0
- Read the full text after 5.7.0 and note the reply code in front of it.
- For relay denials, check the relay configuration and that the sending domain is registered with the service.
- For authentication or TLS demands, enable SMTP AUTH over TLS on port 587; see 535.
- For suspended accounts, resolve the abuse report with the provider instead of retrying.
- For content rejections, remove risky attachments and shortened or redirect links, and scan a sample with the header analyzer.
5.7.0 questions
What does SMTP error 5.7.0 mean?
It means the receiving server permanently refused the message for a security or policy reason it did not classify further. Gmail uses it for relay problems, suspended accounts, authentication requirements and flagged content. The text after the code tells you which.
Is 5.7.0 the same as 5.7.1?
No. 5.7.1 specifically means delivery was not authorized and the message was refused, usually because of reputation, blocklists or recipient policy. 5.7.0 is the undefined catch-all for the same class. Both are permanent and both require reading the text. Sort them by that text, not by code.
Should my server retry after a 5.7.0?
No. It is a permanent failure. Retrying the same message with the same setup gets the same answer. Fix the cause named in the text, whether that is credentials, relay registration, TLS or content, and then send again. Nothing about the code is temporary.