History of Mail and Things Communicating

Recall using mail on the Arpanet in those early days, but it was never seen then as a means to stay generally connected.  Only to answer very specific questions.

Network Trailblazer: A Conversation with Eric Allman
Eric Allman talks about Sendmail, the first "killer app" for the networked age, and gives an update on his  work with the Internet of Things ...

If he had known that most of the email he would receive every day would be unsolicited bulk email, he might have done things differently. Network Trailblazer Eric Allman was the author of delivermail, and its successor sendmail. Delivermail was the mail transport agent (“MTA”) first shipped in 1979 as part of 4.0BSD, a UNIX operating system developed and distributed by the Computer Systems Research Group of the University of California, Berkeley. ... "