Go to Tools Options
The Preferences tab should be selected by default and click on the Junk E-mail button.
From here click the Safe Senders tab and verify a check in the box next to Also trust e-mail from my Contacts. I also check Automatically add people I e-mail to the Safe Senders List, though you will want to be cautious with this one and may want to turn it off if you start getting SPAM.
