x.400 is a communication standard used for transferring EDI messages among business partners and their EDI providers. 

It is an e-mail system whose network consists of x.400 mutually interconnected operators. These operators take care of the sending and distribution of messages. 

x.400 system is an ideal tool for transmitting data in various formats in the environment that places high demands on the security of the transmission – besides EDI, it can be used, e.g. in an army.