The recipient's mailbox is temporarily unavailable. This is often due to greylisting or server policies.
SMTP error 450 indicates a temporary condition where the mailbox cannot receive mail right now:
Server delays first-time senders to verify they're legitimate mail servers that will retry.
The mailbox is temporarily locked due to maintenance or quota operations.
Temporary policy-based rejection, often related to sending patterns.
Your mail server should automatically retry. Greylisting typically accepts messages after 5-15 minutes.
Ensure your mail server is configured to retry temporary failures with appropriate delays.
If errors persist, review your sending patterns and ensure you're not triggering rate limits.
450 4.2.1 Mailbox temporarily disabled
450 4.7.1 Greylisted, please retry in 5 minutes
450 Requested mail action not taken: mailbox unavailable