Hasn't happened to me too often. My bro had a doozie though. He got some email from a partner or principal in a law firm, who was attempting to forward it to one of his colleagues in the firm that shared my bro's first name. The kicker was that the email string was about one of the junior lawyers who was disputing what she had been paid for billed hours, and my bro knew her from high school and still does socially. I don't quite recall how the partner had my bro's email address. My bro responded and said hey you've got the wrong email address, I'll just go ahead and delete and forget about this and left it at that, and didn't say anything to the girl he knew. He never got any sort of reply from the law firm about it.
Turns out he runs in to her a few weeks later, and he's just making small talk and not mentioning that he knows how much she made the past few years and how her law firm is trying to fuck her. He asks her how things are going, and she responds to the effect of "well you have an idea I guess, fighting with my firm about my salary and bonus. Thanks for not just deleting that email and actually responding, because it made settling things a lot easier for me!"