Lookup for "450 2.3.4"
This status code indicates a successful delivery or other operation. Any details are simply notes.
Basic Status Code Details (450)
Requested mail action not taken: mailbox unavailable [E.g., mailbox busy]
Enhanced Status Code Details (2.3.4)
Message too big for system
The message is larger than per-message size limit. This limit may either be for physical or administrative reasons. This is useful only as a permanent error.