1. A file belonging to a particular user on a particular computer in which received electronic mail messaGEs are stored ready for the user to read them. A mailbox may be just an electronic mail address to which messaGEs are sent and may not actually correspond to a file if the messaGEs are processed automatically, e.g. a mail server or mailing list. 2. A destination for interprocess messaGEs in a messaGE passing system. A mailbox is a messaGE queue, usually stored in the memory of the processor on which the receiving process is running. Primitives are provided for sending a messaGE to a named mailbox and for reading messaGEs from a mailbox. (1994-10-20)