For me the first E-mail I would have gotten would have been around 1995 when I first went on the internet via American Online. You'd always hear that annoying voice that said, "You've Got Mail." Of course it(the e-mail) was most likely by some scam artist.
My earliest memories though were hanging out in the newsgroups which I guess were the precursor to forums like these. They weren't as organized and spam was all over the place, but there were still some pretty good discussions going. I actually defended Yoko Ono and Linda McCartney once in a Beatles' newsgroup and someone pretending to be Yoko thanked me. Those were interesting times
