How do you unblock a sender on Outlook email?

If you want to stop receiving e-mail from someone, you can add his or
her e-mail address to your blocked senders list. Outlook automatically
moves any new mail that you receive from this person to the Junk E-mail folder. When you want to receive mail from this person again, you can
remove his or her e-mail address or domain from your blocked senders
list.

Do any of the following:

Block a sender

1. In the message list, select a message from the sender whom you want to block.
          
        
2. On the Home tab, click Junk, and then click Block Sender.
3. Outlook adds the sender's e-mail address to the blocked senders list.Note: You can restore any of the mail that is in the Junk E-mail folder. Click the message that you want to move to the Inbox folder, and then on the Home tab, click Junk, and then click Mark as Not Junk.

      Unblock a sender

1. On the Tools menu, click Junk E-mail Protection.
2. On the Blocked Senders tab, in the Blocked Senders text box, select the e-mail address or domain that you want to unblock, and then press the Delete key.

I think this will help you to unblock a sender on Outlook email.

Regards,