Next, the CPYNET code was incorporated into SNDMSG. It remained to provide a way to distinguish local mail from network mail. I chose to append an at sign and the host name to the user’s (login) name. I am frequently asked why I chose the at sign, but the at sign just makes sense. The purpose of the at sign (in English) was to indicate a unit price (for example, 10 items @ $1.95). I used the at sign to indicate that the user was “at” some other host rather than being local.- Alexander Shulgin (Wikipedia)
Alexander Theodore “Sasha” Shulgin (June 17, 1925 – June 2, 2014) was an American medicinal chemist, biochemist, organic chemist, pharmacologist, psychopharmacologist, and author. He is credited with introducing 3,4-methylenedioxymethamphetamine (MDMA, commonly known as “ecstasy”) to psychologists in the late 1970s for psychopharmaceutical use and for the discovery, synthesis and personal bioassay of over 230 psychoactive compounds for their psychedelic and entactogenic potential.