SMTP code 550 5.7.0
What the knowledge base's own tables say about this code, and which articles say it — a description of the reply, never a placement prediction.
This line comes from a knowledge base article on Gmail, not on the standard.
- Message
- "Email relay denied" (invalid credentials or suspended account)
- Meaning and fix
- Register the sending IP address in the Workspace SMTP relay settings, or the relay account is suspended for spam
From Gmail SMTP Errors and Troubleshooting · Content, format, and policy