Email spoofing is forging email so it looks like it came from someone it didn’t. I learned to spoof email in the fall of 1993 during my sophomore year at Northwestern. An upperclassman in my dorm showed me. At that time, we read our email by telnetting into the campus mainframe and then using elm, the precursor to Mutt.
“Look,” he said, “You just change the “From” header to whatever you like. Don’t–don’t–ever do this for real or we’ll both get in trouble.” I never did.