Lookup for "221 5.2.2"
Permanent Error - This status code indicates a permanent issue and is unlikely to resolve itself. You should contact the Email Service Provider.
Basic Status Code Details (221)
Enhanced Status Code Details (5.2.2)
Mailbox full
The mailbox is full because the user has exceeded a per-mailbox administrative quota or physical capacity. The general semantics implies that the recipient can delete messages to make more space available. This code should be used as a persistent transient failure.