X

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XML

Extensible Markup Language.

XSL

Extensible Stylesheet Language.

XSO

Exchange System Objects, an interface first provided by Exchange 2003 to allow programmatic access to Exchange objects.

X.400

The international standard for messaging interoperability that has now largely been surpassed by the combination of SMTP and MIME.

X.500

A comprehensive definition of a standard for enterprise directories. Many directories, including the DS and the AD, are derived from X.500. However, these directories are not fully X.500 compliant, because they do not support the X.500 access protocols.

X.509

A standard for digital certificates used by Kerberos and Exchange advanced security.

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