SMTP 450 indicates a temporary failure like mailbox unavailable or a soft policy block. Learn how to handle retries safely.
SMTP 450 is a temporary error that can mean the mailbox is busy, the recipient server is deferring mail, or a policy check triggered a soft rejection.
Treat 450 as a soft bounce: retry later with exponential backoff. If a pattern appears, investigate content, sending rate, and recipient-specific filtering.