Definition: X.400

An OSI and ITU standard messaging protocol. It is an application layer protocol (layer 7 in the OSI model). X.400 has been defined to run over various network transports including Ethernet, X.25, TCP/IP and dial-up lines. See messaging protocol, XAPIA and CMC. Following is the format of an X.400 address:

  /c=  /admd=  /prmd=  /o=  /s=  /g=


  X.400
  Code     Purpose

 /c=      country

 /admd=   administrative management domain
           (public email service)

 /prmd=   private management domain
           (in-house email)

 /o=      organization

 /s=      surname

 /g=      given name