During the first 30 years of email, different email systems had very different ways of representing content. For example, address formats, and the representation of rich text in the main message, varied. It was therefore difficult to connect different email systems.
The X.400 standards, mainly published in 1984-1988, were an attempt to introduce consistency, and thus facilitate interconnectivity. Concurrently, internet-based email standards were also developed.
By about 1994, the internet-based approach, rather than the X.400/X.500 approach, became dominant. This was mainly due to the:
- Spread of the internet
- Simplicity of using internet rather than X.400 email addresses
- Cheapness of internet mail. With X.400, service providers would charge for email transmission; with internet mail, once you had an internet connection in place, it was free.