An ITU-T specification, published in 1996, describing the handshaking protocol used between Group III/IV facsimile machines to establish and maintain communications.T.30 also provides for routing faxes to users via subaddresses or fax mailboxes. Message security is included, so that only those responsible for certain manual routing processes can view even the cover page. See also facsimile, Group III, Group IV, handshaking, and protocol.