The operating system supports a virtual device, called a mailbox, that is used for communication between processes. Mailboxes provide a controlled, synchronized method for processes to exchange data. Although mailboxes transfer information much like other I/O devices, they are not hardware devices. Rather, mailboxes are a software-implemented way to perform read and write operations between processes.

For additional information about using mailboxes, see HP OpenVMS Programming Concepts and the HP OpenVMS System Services Reference Manual.