Myth buster website, snopes.com, had an interesting story recently about email. It's worth a read.
1) Any time you see an email that says "forward this on to '10' (or however many) of your friends", "sign this petition", or "you'll get bad luck" or "you'll get good luck" or "you'll see something funny on your screen after you send it" or whatever --- it almost always has an email tracker program attached that tracks the cookies and emails of those folks you forward to. The host sender is getting a copy each time it gets forwarded and then is able to get lists of 'active' email addresses to use in SPAM emails or sell to other spammers. Even when you get emails that demand you send the email on if you're not ashamed of God/Jesus --- that is email tracking, and they are playing on our conscience. These people don't care how they get your email addresses - just as long as they get them. Also, emails that talk about a missing child or a child with an incurable disease "how would you feel if that was your child" --- email tracking. Ignore them and don't participate!
Honestly, aren't we getting enough unwanted email every day without making it easier to be reached.