Oh fer feck's sake. I'm going to channel Samuel L. Jackson's character from a Time to Kill and say people who don't know the difference deserve to
There was a one page attachment that explained that "Reply" sends a response to the sender, and "Reply All" sends a response to everyone who got the message AND the sender. It went on to explain distribution lists and choosing wisely when you select "Reply All." I would say everyone should know this already, but then again, if this is being sent out as a "helpful IT tip," I might be wrong.
It's happened before.