Unfortunately there are many worms, viruses, and spammers that can use your email address when they send their email. If those emails generate errors then you receive those error messages - even though you did not send the message. The "From" address of an email is not used by any of the mail servers the email transits unless there's an error so anyone can use any "From" address when they send their email, and there's no means to prevent them from doing so. If you receive a very large number of these notices in a short period you can use the CCC to create Filters to automatically delete the messages when they come in. You would only want to use these filters temporarily as needed - otherwise legitimate error messages you would ordinarily want to receive could be deleted as well.