A multi-segment message is composed of two or more message segments. Each segment is passed individually to JES XCF through an IXZXIXSM (send message) macro invocation. Although JES XCF doesn't deliver the message to the receiver's mailbox until all message segments have been sent, the receiver retrieves the message from the mailbox one segment at a time. Because the segments are sent and retrieved individually, you can use this exit to change or add to segments individually. If you inadvertently make inconsistent changes to two or more segments, JES XCF uses the changes made to the first segment only.