Status 1#
smtp;421 Service Temporarily Unavailable
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.
Spam filter · 4.x.x transient failure
Email Security.cloud SMTP 421 Errors: Every Bounce Response Explained
Every SMTP 421 response on record from Email Security.cloud, 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
- Email Security.cloud
- Code
- 421 (4xx)
- Responses
- 1
- Highest severity
- Unclassified
Email Security.cloud SMTP 421 responses
Email Security.cloud SMTP 421 questions
›What does an SMTP 421 error from Email Security.cloud 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 Email Security.cloud, 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 Email Security.cloud 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 Email Security.cloud's postmaster documentation.