Sending e-mail to others with your e-mail address exposed is another way to get more than you want. A friend started including me in his circle of friends where everyone could see everyone else's e-mail address. Before long someone had an e-mail virus that stole all of their e-mail recipients and I was bombarded with the same sorts of pharmaceutical, dating and other unwanted e-mails. My e-mail provider went belly up and I quit sending e-mail to the friend from my new address. Problem solved.
If you send an e-mail to a group, put them all in BCC instead of "To" or "CC" so no one can see the other recipients. It's not a 100% solution but it's a good start.
David