The below are results when doing an mta-stats, i have cleared these number of times and these continue building (Delivery_queue_Msgs)
The users don't claim sending any emails. The delivery queue is fine but the Deferred queue seems to get bigger.
delivery_connections: 25
delivery_data_rate: 6199 bytes/sec
delivery_deferred_msgs: 299
delivery_msg_rate: 0 msg/sec
delivery_queue_size: 7246 KB
delivery_queued_msgs: 322
inbound_deferred_msgs: 0
inbound_listener_connections: 2
inbound_listener_data_rate: 6141 bytes/sec
inbound_listener_msg_rate: 0 msg/sec
inbound_queue_size: 0 KB
inbound_queued_msgs: 0
outbound_deferred_msgs: 0
outbound_listener_connections: 0
outbound_listener_data_rate: 0 bytes/sec
outbound_listener_msg_rate: 0 msg/sec
outbound_queue_size: 0 KB
outbound_queued_msgs: 0