Click on "My Settings" in the top right hand corner.
Click on either the Aprrove Senders or Block Senders link:
Enter email addresses into the left hand side box, separated with a comma: (,), a colon: (:) or a line break between each email address. After you have finished entering email addresses to be approved\ blocked, click the Update Blocked\Approved Senders button.
If you wish to block domains, use the right hand side box to blacklist entire domains, such as hotmail.com. Enter multiple domains separated using a comma, colon, or line break, and then click the Update Blocked Domains button.
After clicking one of the update buttons, the server will display a message indicating that the update was or was not successful.