X-headerUser-defined, unofficial header field that exists in the message header. X-headers are not specifically mentioned in RFC 2822, but the use of an undefined…
X.400 ConnectorAn Exchange component that is integrated with the message transfer agent (MTA) and can be configured to connect routing groups within Exchange, or to…
X.400 RecommendationsDefines the standard interfaces of an electronic messaging system. These recommendations specify the structure of a message handling system, message…
X.400 transport stackNetworking software required to support X.400 server-to-server message transport. [Exchange 5.5]
XML (Extensible Markup Language)A markup language that enables users to tag data in order to delimit it, leaving the interpretation of the data to the applications that read it.