Mailbox Availability

Once a mailbox is built, that mailbox is available to receive mail until one of the following events occur:

The system on which the JES member resides is re-IPLed.
After re-IPLing, the member should rebuild its mailbox. JES XCF resends all messages sent by other members, except those of REQTYPE=COMM, that were in the mailbox at the time the system was shut down. Your JDU must access that mailbox to determine if these messages should be received and processed or deleted. JES XCF sets the RESENT_DUE_TO_IPL bit in IXZYIXEN (the message envelope) for each message that was in the mailbox prior to termination. Consider the age and interim system events when deciding the disposition of such "resent" message data.
A member associated with the mailbox issues the IXZXIXDT macro to become an inactive member of the related XCF group.
Messages sent to a member that has been detached cannot be received by that member until it becomes a member of the XCF group again. Any messages in the mailbox at the time of the detach are acknowledged by JES XCF with a return and reason code indicating the message is acknowledged because the receiver has detached from the XCF group.
The IXZXIXMD macro is issued to delete the mailbox.

If, after you build a mailbox, JES terminates with a termination that does not result in a detach (that is, in JES2, a $P JES2 ABEND; or in JES3, a *RETURN), the mailbox is still available to receive messages. JES code running in another address space or on another JES can continue to send messages to the mailbox. When JES restarts, the mailbox will contain messages that were sent to the mailbox while JES was down, as well as messages that were in the mailbox when JES terminated. JES XCF sets the MESSAGE_RESIDUAL bit in IXZYIXEN (the message envelope) for each message that was in the mailbox prior to termination. Use this indicator to determine if the message is "old" or "new".

The routine that retrieves messages from the mailbox should then decide whether to clear messages from the mailbox or receive and process them.