Hello SIGCIS, Our of the last unsourced footnotes for the Revised History of Modern Computing holds a note to myself concerning a possibly exaggerated factoid from the "Hobbes' Internet Timeline." https://www.zakon.org/robert/internet/timeline/ According to the timeline entry for 1973: "ARPA study shows email composing 75% of all ARPANET traffic." Keep in mind that Tomlinson sent the first network mail in 1971 and mail technologies were rather immature for the first few years. If that is true it's certainly a fact worth including in the book to demonstrate the very rapid spread of email on the ARPANET. But "ARPANET study" is not something I can use to confirm the original source. I haven't been able to find anything so specific in Janet Abbate's book Inventing the Internet though she features email prominently and agree that its rise was both rapid and unexpected. Ian Hardy's undergraduate thesis, an early historical look at Internet email, does not include this particular figure. https://www.livinginternet.com/References/Ian%20Hardy%20Email%20Thesis.txt Craig Partridge's IEEE Annals article "Technical Development of Internet Email" didn't, on a recent skim, seem to say anything on this topic either. Does anyone know where this number might be coming from? Or have a well-sourced alternative for slightly later year like 1975 or 76? Best wishes, Tom