Question 163. What is X.400?

ITU-T Recommendation X. 400 [CCI88a], also known as the Message Handling System (MHS), is one of the two standard e-mail architectures used for providing e-mail services and interconnecting proprietary e-mail systems. The other is the Simple Mail Transfer Protocol (SMTP) used by the Internet. MHS allows e-mail and other store-and-forward message transferring such as Electronic business Data Interchange (EDI, see Question 164) and voice messaging. The MHS and Internet mail protocols are different but based on similar underlying architectural models. The noteworthy fact of MHS is that it has supported secure messaging since 1988 while the Internet is still considering a variety of draft standards such PEM (see Question 130), S/MIME (see Question 131), and PEM-MIME (see Question 132). The MHS message structure is similar to the MIME (see Question 133) message structure. It has both a header and a body. The body can be broken up into multiple parts, with each part being encoded differently. For example, one part of the body may be text, the next part a picture, and a third part encrypted information.