What This Error Means
The mailbox is temporarily unavailable. This is often a greylisting response where the server asks you to retry later to verify you're a legitimate sender.
Common Causes
- 1Greylisting in effect
- 2Temporary server issues
- 3Rate limiting
- 4Server maintenance
How to Fix It
- 1Retry after 5-15 minutes (greylisting)
- 2Implement proper retry logic
- 3Ensure your mail server handles 4xx responses correctly
- 4Monitor retry success rates
Quick Reference
- Error Code
- 450 4.1.1
- Category
- Temporary Failure
- Severity
- Low
- Should Retry?
- Yes, with backoff
View All SMTP Errors