What is a X.400?
X.400 is a standard definition of data communication for messages used for email. During its creation, its designer thought it would become the global standard for email. However, it was overtaken by the SMTP standard for email communication.
Even though it is not the primary form of email communication, it is still used in some organizations and software including Microsoft Exchange Server. An X.400 address consists of several elements about a partner, such as: C (Country name), ADMD (Administration Management Domain), PRMD (Private Management Domain) O (Organization Name), OU (Organization Unit Names), G (Given name), I (Initials), S (Surname).