http://www.rfc-editor.org/rfc/rfc4155.txt
RFC 4155: The application/mbox Media Type, E. Hall2005-09-01T23:00:00-00:00This memo requests that the application/mbox media type be authorized for allocation by the IESG, according to the terms specified in RFC 2048. This memo also defines a default format for the mbox database, which must be supported by all conformant implementations. This memo provides information for the Internet community.