I did a quick search and didn't come up with anything. I'm sure the answer is here somewhere but I have an oops.

I just used the System Email Users function and choose the "Moderators" group and checked the only send to users that accept option. The mail went to every user (maybe everyone minus the users that checked privacy). I don't have 100 moderators.

I then sent an apology message and checked Moderators again to be sure I didn't miss the option earlier. It went to everyone again.

I'm sure I used this before and checked Webmasters which had worked. Now I'm afraid to use the function again until I know what happened.