SMTP code 550 5.1.1
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.
- Test that tells causes apart
- Is it one address or many? One points to a typo or a churned address. Many point to a list-quality problem
- Next step
- Suppress the address (a hard bounce means permanent suppression). If many: audit the acquisition source and see list hygiene
- Rejection says…
- "user unknown", "mailbox does not exist", 5.1.1, 550 5.1.1
- Hypothesis
- Invalid recipient
From Delivery Troubleshooting Playbooks · Playbook A: message not delivered (bounced or rejected, 5xx)
This line comes from a knowledge base article on Gmail, not on the standard.
- Message
- "The email account that you tried to reach does not exist"
- Meaning and fix
- Hard bounce: remove the address and check for typos
From Gmail SMTP Errors and Troubleshooting · Recipient and addressing