I just found out that I was banned from answering questions today. I contacted the team and luckily I received an answer quite fast (the same day, thanks btw), which I wasn't expecting. It seems like the problem was that I posted comments as answers, so my bad. To be honest I started using this site when google started sending me here more and more, and at first at least, I didn't pay much attention to all of the features, so to speak.
The problem is that I wasn't at all aware of the issue until I got banned. There was no notification, no warning, nothing. In hindsight, I should have read the FAQ and I should have took the time to learn how the site works. But still, I presume this kind of thing happens quite often. And it's unpleasant to both the person getting banned, and the person dealing with the complaining email.
So my suggestion would be to send a notification when someone is getting close to being banned, possibly with a link to the documentation about how to avoid it. Now if my situation is unique it's not worth the trouble, but as I said, I presume it's not. If you guys feel that such a thing might help people figure out the system, another option is to send notifications when someone is doing something that might get them banned. For example if your answers are getting deleted or if you get more than a certain number of vote downs. I realize these are obvious things to avoid, but from my personal experience I can tell you people might not realize that it's happening, or how serious it is.