Do you have OS X Server installed on your machine? After monkeying around with this for a couple of days, I was trying to fix my password in mail preferences per one of these forums; but when I tried to save the settings I got a pop-up stating something about a conflict between two servers.
Last week I purchased and installed the OS X Server with the intent to set up a home server to allow friends access to large file transfers. That's a whole different thread, but for a "quick start" I had no joy. While I kept the server installed, I had all "services" disabled. I don't know how it fixed it; but I deleted the OS X Server from the machine, restarted, and now all three AOL accounts can recieve and SEND! The server problem will have to wait for another day... :-) Good luck!