I found this answer on puzzlenyc.org:
Unfortunately, it doesn't look like you can select a group of messages that
are already in your Junk mail folder and add them to your blocked sender list.
However, you could eliminate most, if not all, spam by adjusting the Junk
Mail filter options. Click Tools > Options. Make sure that you are on the
PREFERENCES tab. Click the JUNK EMAIL button.
The first tab lets you set the general filtering level. You may want to
adjust the level and make it higher. Personally, I use the highest level
meaning that I only want to see mail from people in my "Safe Senders" list.
Yes, it does mean that sometimes, mail that I really do want gets placed in
the junk mail folder. But, if that happens, I then add those names to my safe
sender list. At least at the highest level, all the spam gets put in the junk
mail, and I have far less to sift through.
You may want to look at puzzlenyc.org under the "technology" discussion
groups section. There are a lot of answers relating to Outlook as well as
other MS Office packages. Many of the answers contain useful links to free
on-line tutorials that Microsoft offers. There are a few good ones directly
related to Spam filtering in Outlook.