My story:

A few years back, I had a couple friends who were dating, and were long distance.

One night the guy comes online telling me this story about how he went out with some friends to a bar, and met a girl. She was into him and he got tempted and they got a room, and she started blowing him. But after less than a minute he felt really guilty, and had her stop and he left. He said he felt really guilty and asked for my advice on what to do. I sat down and thought things through and talked him through it. I felt pretty good about myself, being there for a friend.

Couple months later, he and I are talking again, and he drops it that he made the whole thing up. He said he was trying to see how I would react. He was pretty cavailer about, like if it was no big deal, just jokes, and like I was overreacting for being pissed. When I mentioned to the girl about it, even worse attitude, playing babe in the woods, and like I was making a mountain out of a molehill.

I greatly reduce contact with them trying to process just how fucked up this was. Basically I realised they felt they could treat me like shit and expect me to smile and take it.

After a while I get an idea. The girl had a very bad reputation for sleeping around in the past (we were all 20ish then, so at the time, a girl's high school sex antics are still fresh in memory). I also knew that a lot of his friends and family did not approve of their relationship because of her past.

I got to work. I gathered up a bunch of email addresses both from his side and her side. This was in the days of email forwards, so it was easy to look at the forwarding history of what I got from them and get the info. I then typed up an email going into her past in detail, and about how she was a slut playing good girl for a nice guy now, and how she was full of shit. After I felt it was just right, I used a throwaway email account and sent it to all the email addresses I gathered.

Shit hit the fan. She freaked the fuck out trying to figure out who sent it, and I was one of the people she suspected. His family didn't come out in support, but rather encouraged him to dump her after it. She was suspicious enough of me to try and get people to add me on messenger and try to talk to me and get me to slip up, but I kept my cool. When I found out for sure that the people who added me on messenger were acting on her behalf, I acted like I was furious with her and blew the fuck up on her. I even turned him against her a bit because he got mad at her for trying to get people to harass me. It was an amazing rush, I was guilty like hell, but she had no proof and had no defense when I went apeshit on her, she meekly took it.

Few weeks pass and both of them start falling back into their snide attitudes with me. I start getting the idea to rock them a part II, and draft it up. Before I can finish it up, she gets in a car crash and is seriously injured. Abort plan.

All my animosity with the girl disappeared like nothing after that, and we grew to become very close friends, with me keeping my secret that it really was me behind that email and her suspicions of me were right. The guy we kept talking, but he was an asshole still and we eventually lost contact, and he eventually left her for another girl (who in turn left him).

I think back to that time, and I feel sure that I was getting sloppy. I think for sure I would have goofed the second email I had planned and gotten caught, and in turn ruined my reputation. Her getting in that car crash saved me from humiliating myself.

TL;DR: I was getting progressively bolder with revenge emails and was likely on my way to getting caught, until the recipient got gravely injured in a car crash.