Obviously you are being spammed. Here are a few steps you can take to try and avoid spam.
1. Don't open unsolicited Spam. Often what happens is that when you open up spam, it sends back a trigger to the originating source indicating that a valid email address has been found thus subjecting you to even more spam down the road.
2. Don't use the Preview Pane for the same reasons as #1
3. Set you email options to accept mail from only people in your address book or safe lists.
4. Set some filters to automatically route spam to certain folders for easy deletion later.
5. Use a throwaway account for any online registrations you need such as news sites and contests, etc. Often these email addresses are sold to other places, particularly advertising firms. If the throwaway account gets over run, you can simply delete it and create another.
6. Use the BCC when composing emails and encourage your friends to do the same. What this does is protects mailing lists from email harvesters.
7. You can consider using a third party application such as SpamFighter (free version can only be used for 1 account and it is for Outlook and Outlook Express only) http://www.spamfighter.com/ . Mailwasher is also a good antispam tool. http://www.mailwasher.net/
8. Never reply to any spam email that you happen to open and receive for the same reason as #1 above.
You can see more info at the webpage below:
http://www.us-cert.gov/cas/tips/ST04-007.html