Block a mail sender - support.microsoft.com
support.microsoft.com › en-us › officeTo add a specific sender to the Blocked Senders List, click a message from the sender. On the Home tab, in the Delete group, click Junk and then click Block Sender. To add names to the Blocked Senders List: On the Home tab, in the Delete group, click Junk, and then click Junk E-mail Options. On the Blocked Senders tab, click Add.