When you build a mailbox, you have the option to request that you be notified when XCF events occur that affect your JES XCF group. You might use this option, for example, if your JDU needs to be aware of any state changes that affect JES members of your JES XCF group.

When the system returns XCF event information, the information is returned to your mailbox in the form of a system event message. To map a system event message, use mapping macro IXZYIXSE. To request notification of XCF events, code SYSEVENT=YES on the IXZXIXMB macro.

A system event can be either a JES or XCF event. Each system event message contains an envelope. The envelope (IXZYIXEN mapping macro) consists of the header data associated with a message. It contains the delivery information that is required to correctly deliver the message to the specified receiver. Mapping macro IXZYIXSE specifies that the event is either a JES event or an XCF event. If the event is a JES event, then mapping macro IXZYIXJE contains the JES data; if the event is an XCF event, mapping macro IXCYGEPL contains the XCF data. Refer to z/OS MVS Data Areas, Vol 5 for the IXZYIXEN mapping and the mappings for the other mapping macros discussed here. Also refer to Figure 1 for a pictorial view of the message envelope (IXZYIXEN mapping macro), and a system event's message structure.