To block an email sender in Outlook find the message that includes the sender you want to block.
Right click on the message
Near the bottom of the pop-up menu you will see "Junk"
Hold the cursor over "Junk" and another window should appear to the right of that.
Select "Block Sender"
That sender will now be blocked from sending further mail to your inbox.
If you ever block a sender by mistake, simply right click on any message select "Junk" then once the menu to the right appears select "Junk E-mail Options..."
Within "Junk E-mail Options" select "Blocked Senders" it is the 4th tab over.
Highlight the sender that is needing removed and select "Remove".
The option to Manually Add a sender is available as well.
Within "Junk E-mail Options" > "Blocked Senders" select "Add..."
A pop-up window will appear.
Enter the email address that needs blocked.
That will now be added to the list of "Blocked Senders"