Configuring preferences and options in Outlook.com
Sorry to hear that you’re having trouble with this situation. Could you please share a little more information about what happens when you try to remove the email address from the Blocked Senders list? Also, how long has the address been on the blocked list? If possible, please share a screenshot of any error message or notification you receive when you attempt to remove it. This will help me better understand what may be causing the issue.
As a test, please try signing in to Outlook.com using an InPrivate/Incognito window.