Argh. That red book. I may still have my copy around, somewhere.

X.400 was an “all things, to all men” solution; kinda like TIFF, for images.

I worked on an X.400 product, that never got out of the crib.

You could do things like specify the route that the email took, which was important, because there was support for microtransactions, all along the way. You could do things like pay extra for “premium delivery,” and “registered”-like messages.

It was really crazy. It did work, though.

The issue with specs like that, however, is they only ever get partially implemented. If you have an infrastructure, composed of many partial steps, it can be a mess.