Most "good" junk mail has an option, usually in small print at the bottom of the page to opt out of future mailings. I use this method all the time and it usually works. For really nasty or unethical junk mailers -
If you have Outlook (don't know about OL Express)
On the toolbar, click Organize.
Click Junk E-mail.
At the bottom of the pane, click the link.
Click the Edit Junk senders link.
Use Help to look up "Junk Mail" to see other features.
The two rules for success are:
1. Never tell them everything you know.