Worth noting is that @ was not the universal separator for host and username. BITNET (and its sister networks) based on IBM’s networking protocols used with word “AT” (separated by spaces) so, back in the olden days I was U12921 AT UICVM. UUCP placed the host name first and used ! to separate the hostname from the user with explicit routing occasionally given by multiple !s to separate a list of machines, e.g., foo!bar!jarthur!dhosek And the DECNET protocol used :: with the host name first (e.g., YMIR::DHOSEK) It wasn’t until the grand unification of all the various academic and commercial networks in the late 80s with the “net of nets” which became the Internet that @ became more universal, although IBM systems retained their “AT” and VMS systems had the awkward IN%"dhosek@ymir.claremont.edu" syntax to allow emailing outside the local DECnet.