How to allow IM messages from someone you've previously blocked.

If you have previously blocked instant messaging conversations with a user and you now want to be able to chat with that person, you can unblock him:

1. Sign in to Yahoo! Mail.
2. Click the gear icon () in the upper-right corner of the window, and select Messenger Options from the menu that appears. A pop-up appears with the Messenger Options menu.
3. From the categories on the left, click Privacy.
4. From the list of blocked users, select the user you want to unblock and then click the Remove button.
5. Click OK.

You can now both receive messages from that user and send messages to him.