What does 452 mean?

SMTP 452 indicates storage limitations:

What it means:

The receiving server or mailbox does not have enough storage. This could be a system-wide issue or specific to the recipient's mailbox.

Common causes:

Mailbox quota exceeded: User's inbox is full. Server disk full: System-wide storage issue. Message queue full: Too many messages waiting.

Typical message examples:

"452 Insufficient system storage" "452 Mailbox full" "452 Too many recipients"

Response:

Retry later. User may delete messages and free space. Persistent 452 on specific address may warrant escalation to soft-to-hard bounce conversion.

452 is a full parking lot. Wait for someone to leave, or accept that this destination may be permanently unavailable.