Years ago, an employee accidently sent an email criticizing me TO ME rather than to the employee he intended to send it to. My first reaction was to be hurt. Next, I was angry. After spending time thinking about how to handle the situation, I simply replied to the author of the email that I thought he meant to send the email to someone else. Almost immediately, he emailed an apology saying he was very disappointed in himself. Perhaps I should have responded but did not.
Personally, I would have felt the need to apologize in person but we are so tangled in a digital world that most would have felt absolved by sending an apology via email.
Although he apologized, I can never fully trust him again. As a result of this situation, I try to remind very mindful of others when I use digital media.