In 1993, a friend of mine was working at Apple. I wanted to send him a funny message with a spoofed sender. I just typed "telnet apple.com 25" and then typed in the required commands. Apple.com accepted it and delivered it to my friend with a fake sender.
Those were the days, lol!
My friends and I used to do this all the time in that same time period. It was all fun and games until one day I caught one of them spoofing a message from me to president@whitehouse.gov making vague threats. He seemed to think I overreacted when I dove under the desk and unplugged the machine.