Do you receive emails from friends where they're sending it to many people, and you see your email address listed among that long list? That obviously means all those people will be able to see your email address. It may not be a problem for those individuals to see your address, but it is possible for one of them to be infected with a virus that can harvest email addresses for Spammers or send you a copy of a virus.
The best solution is to use the "BCC" in your email to protect the email addresses of your friends. Most all email programs will have "To" and "CC" options visible, but you may not see the "BCC". Generally, to get the "BCC" active, start a new email and click on "View". Note that this is NOT under the main email program that lists your emails, but under the menu choice in a new email itself. The exact steps will vary depending on the email program you're using and the revision. Give us a call if you need assistance.
So, if you're getting emails from others that lists your address in a long list that you can see, just ask them to start using the "BCC" option. It's your email address...best to protect it!