Transient (4xx)
452 4.2.2
Mailbox full (temporary)
The recipient's mailbox is over its storage quota right now. The address is valid; mail is accepted again once they free up space.
452 4.2.2 Mailbox full
What it means in practice
The recipient's mailbox is over its storage quota. Their address is real, and mail will be accepted again as soon as they free up space, so this is a deferral, not a bounce.
If the same address keeps returning 4.2.2 for days, the mailbox is probably abandoned. Many providers eventually switch to the permanent 552 5.2.2 for it. Treat repeated 4.2.2 over a couple of weeks the same way: suppress the address and stop retrying.
Common causes
- Recipient hasn't checked or cleaned up their inbox.
What to do
- →Retry later - this often clears once the recipient frees up space.
- →If it never clears, treat it like a soft bounce and eventually suppress the address.