Colin Berkshire writes:
The invention of email is widely credited to be Ray Tomlinson (http://en.wikipedia.org/wiki/Ray_Tomlinson) in 1971. In one especially oddball webpage, VA Shiva Ayyadurai claims to have actually invented email in 1978. (http://www.inventorofemail.com). Mr. Ayyadurai mostly substantiates his claim by playing games with the definition of what email is, basically arguing that email didn’t exist until his particular program was written, and that nothing beforehand actually amounted to what he defines as being email. I won’t play those games with you here. [...]
And, the #1 ESS ADF was in full production service February 3, 1969…almost five years before Ray Tomlinson sent the first email message and well before ARPANet even existed. To clarify, that was full commercial service…not a research laboratory.
When the #1 ESS ADF system was cut into service in 1969, it was of a truly massive scale for the time. 1,250 terminals located in 720 locations across the country were connected. These were used by Western Electric and AT&T Long Lines to send administrative messages, traffic orders, commercial service orders, payroll, plant service results, and budgeting reports. There was no other system, including universities, with such widespread use.
Full Story: Cloudave: The Origin of Email
The system is described in the Bell System Technical Journal in 1970, and is also mentioned by Jim Haynes in an essay on Teletype Corporation.