When querying the Message Queues page of the Control Center web interface, some messages are queued in the Inbound queue with the error: 421 4.7.7 [internal] Unable to process message at this time.
Querying the message queues from the command line via the mta-control command to query queue also shows the same issue. On further review of the mail log, there are errors stating “Deferring message: failed to filter message” .