450 Requested mail action not taken: mailbox unavailable

Meaning

The mailbox was unavailable (e.g., mailbox busy).

Common causes

• Mailbox locked.
• Temporary routing issue.

How to fix

1. Retry later.

Example bounce

450 Requested mail action not taken: mailbox unavailable

Related codes

• 450 4.2.4 Mailing list expansion problem
• 452 4.2.2 Mailbox full (temporary)
• 501 5.1.3 Bad destination address syntax