Lookup for "552 4.4.6"
Temporary Error - This status code indicates a transient issue and may resolve itself.
Basic Status Code Details (552)
Requested mail action aborted: exceeded storage allocation
Enhanced Status Code Details (4.4.6)
Routing loop detected
A routing loop caused the message to be forwarded too many times, either because of incorrect routing tables or a user-forwarding loop. This is useful only as a persistent transient error.