I've been using an AOL email address since 1992; while I've been trying in recent years to move everything to a private domain email address, I have so many contacts who still use my AOL address I can't get rid of it.
Every version of Mail.app going all the way back to the beginning has worked fine with AOL, using POP or IMAP. (One thing to be aware of: If you use IMAP, AOL will delete email from the server after about 20 days. I use a Rule in Mail that says "if any part of the To: address includes aol.com, move the message to a folder called Saved Mail on my local hard drive.)
The server settings are:
Incoming mail server: imap.aol.com
Username: Your AOL username (without the @aol.com part)
Password: Your AOL password
Outgoing mail server: smtp.aim.com
Use custom port: 587
Authentication: password
Username: Your AOL username (without the @aol.com part)
Password: Your AOL password
Turn on the "Use only this server" checkbox
