PRMMBX is a privilege that allows a process to create or delete a permanent mailbox by executing the Create Mailbox and Assign Channel ($CREMBX) system service or the Delete Mailbox ($DELMBX) system service. The privilege also allows the creation of temporary mailboxes with the $CREMBX service.
Mailboxes are buffers in virtual memory that are treated as if they were record-oriented I/O devices. A mailbox is used for general interprocess communication. Do not grant PRMMBX to all users of the system. Permanent mailboxes are not automatically deleted when the creating processes are deleted and, thus, continue to use a portion of system dynamic memory. System performance degrades as system dynamic memory becomes scarce.