If you are using webmail, log in and go to Settings. Under the Spam Controls category you will see under the “Spam Filters by Address" section a list of all accounts that are currently blocked. Type in the addresses or domains you want to block and click the green “+" sign.
If you are using the AOL software, click on the Mail drop down menu. Click then on "Block Unwanted Mail." From the window that renders, click on Edit that located next to "Sender Filter." It's located near the bottom.
Then from the next window, click on the link "Use a Custom Sender List." Once you click on the link you will be presented with a list of currently block addresses to which you can add or remove addresses.