Using Object Mailboxes
Before a mailbox can be used, it must be created; typically, this is done by the receiving thread, so that thread must be created first; alternatives are to create the mailbox in the initial thread or to use object directories.
The response mailbox parameters for the acknowledge portion of the transaction can be NULL_RTHANDLE if no further response is required at this point.
(This is application specific and could change depending on the system design.)