Not only did my math master's thesis adviser use Linux, he read his email from a command line program and wrote his papers in plain TeX, considering LaTeX a new fangled tool he didn't need.
plain TeX is a joy to use, but you must really understand boxes and glue etc on a deep level. LaTeX makes that easier, but at the cost of extreme complexity internally (compare the output routines for example.)
my whole university email server was accessed via telnet.
So everyone used tty for email.
I think there may have been a gui or mail app that you coud point to it, but no one did.
There was about a million(trillian?) gui's people used for icq messaging though.
it might've been ssh i can't really remeber. The library catalog was maybe the telnet one.
IIRC don't think either service was accesible via the internet though.
I set up Alpine to read my Gmail last summer, and while the nostalgia hit was nice, the browser version was more responsive and useful, cap I went back to that.