Just in case you think the military has a monopoly in this business. Defense Messaging System program Book reading Chapter 4. Application layer protocols. Internet Mail Consortium pages with lots of e-mail development information. 19 April 99 Quality of Service outline.
Internet history notes.
The development of the Internet has an interesting history. This fast sketch provides places to dig further. Another Internet timeline. This one has somewhat more detail and references. Book reading Networking is the Foundation.