SMTP code 550 5.2.1
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.
The knowledge base documents this code in more than one row. What tells those rows apart is the rejection text in your own log, not the code: read each line below against what your rejection says.
This line comes from a knowledge base article on Gmail, not on the standard.
- Message
- "The email account that you tried to reach is inactive"
- Meaning and fix
- Disabled account; suppress it
From Gmail SMTP Errors and Troubleshooting · Recipient and addressing
- Message
- User "is receiving email at a rate that prevents delivery"
- Meaning and fix
- Rate limit on the recipient
From Gmail SMTP Errors and Troubleshooting · Recipient and addressing