smtp;421 Temporary failure, please try again later.
You are sending faster than this receiver currently accepts from you. Slow down and the automatic retry will deliver the queued mail.
Spam filter · 4.x.x transient failure
Barracuda SMTP 421 Errors: Every Bounce Response Explained
Every SMTP 421 response on record from Barracuda, with the verbatim text, the enhanced status code, a severity rating and a plain-English fix.
The service is temporarily unavailable and the connection is being closed. The receiver is telling the sender to back off and reconnect shortly. It usually comes from rate limiting, a full queue, or a brief reputation check on an unfamiliar sender.
- Spam filter
- Barracuda
- Code
- 421 (4xx)
- Responses
- 2
- Highest severity
- Low
Barracuda SMTP 421 responses
smtp;422 License Expired
The receiver deferred this message and will retry it automatically. A failure that sticks around usually traces back to rate limits, reputation, or a policy on the receiving side.
Postmaster & documentation
Barracuda SMTP 421 questions
›What does an SMTP 421 error from Barracuda mean?
The service is temporarily unavailable and the connection is being closed. The receiver is telling the sender to back off and reconnect shortly. It usually comes from rate limiting, a full queue, or a brief reputation check on an unfamiliar sender. At Barracuda, it is a temporary deferral that is retried automatically, and the specific reason is in the enhanced status code and message text of each response below.
›How do I stop Barracuda from returning SMTP 421?
Match your bounce text to one of the responses below and follow its guidance. Recipient-side wording means fix the address. Authentication or reputation wording (SPF, DKIM, DMARC, blocklist) means fix your sending setup, and check Barracuda's postmaster documentation.