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X.400

An international message-handling standard for connecting e-mail networks and for connecting users to e-mail networks. X.400 is published by the International Telegraph and Telephone Consultative Committee (CCITT) standards body, now called the International Telecommunications Union (ITU). The X.400 Application Programming Interface Association (XAPIA) defines programming interfaces to X.400. MAPI applications are fully interoperable with X.400 messaging applications.

X.435

An international message-handling standard that is published by the International Telegraph and Telephone Consultative Committee (CCITT) standards body, now called the International Telecommunications Union (ITU), and that implements the Electronic Data Interchange (EDI) standard for integrating data with various native formats into a message.

X.500

An international message-handling standard for directory services, published by the International Telegraph and Telephone Consultative Committee (CCITT) standards body, now called the Internal Telecommunications Union (ITU).

X.509

An international message-handling standard for message authentication and encryption. X.509 is published by the International Telegraph and Telephone Consultative Committee (CCITT) standards body, now called the Internal Telecommunications Union (ITU).

Xapia

The X.400 Application Programming Interface Association, the standards-setting body for programming interfaces to X.400 components. XAPIA also defines the Common Messaging Calls inteface component.