Uh, you could email many more people on compuserve and Fidonet then than were on the Internet at all.
BBSes had that kind of email long before there was any move towards the Internet.
What's uh? Compuserve had email, but it was not Internet connected nor SMTP, where did I say or imply otherwise. And a BBS in the 1980s wouldn't ask you for your "email" address.
Yes, they would and it was called email regardless of whether it was SMTP.
You could enter your FIDONET address or some other similar thing when you created an account to link them.