Messages in the delivery queue that are destined for the spam quarantine are not able to be delivered.
451 4.4.1 [internal] connection was not attempted: domain is marked down
421 4.4.0 [internal] no MXs for this domain could be reached at this time
The quarantine port is not available due to an issue with the Control Center (CC) service.
Test the connection from the scanner to the control center.