The PMDF message circuit checking facility may be used to monitor the health of the PMDF system and of other e-mail connected systems, by periodically looping messages through (back to the circuit check facility) and monitoring on the delivery time for the loop to complete.

The PMDF manager configures the facility to periodically send messages to loopback addresses (addresses that will loop through PMDF channels or remote systems and come back to the circuit checking facility). The sizes and other aspects of such messages may be controlled. A circuit check detached process runs, that wakes up periodically and sends out circuit messages and looks for which circuit messages have arrived back. And the facility maintains binned counters for the lengths of time the messages take to complete their circuit. Thus the components are:

• The circuit check configuration file, controlling what sorts of messages are sent where and when.
• A circuit check channel definition in the PMDF configuration file, and an alias pointing to the circuit check channel address.
• The circuit check detached process.
• The database of circuit completion counters.
• The PMDF CIRCUIT_CHECK/SHOW (OpenVMS) or pmdf circuit_check -show (UNIX or NT) utility which may be used to display the values in the circuit completion counters database.