Outlook
To block a sender right-click on a message from the sender you wish to block then click on Junk > Block Sender.
To unblock a sender click on the Home tab then click on Junk > Junk E-mail Options...
Click on the Blocked Senders tab then select the email address of the sender you wih to unblock, click Remove, then click Apply.
Outlook Web
To block a sender right-click on a message from the sender you wish to block then click on Block.
To unblock a sender go to https://outlook.office.com/mail/options/mail/junkEmail. Click on the trash can icon next to the email address of the sender you wish to unblock.
