I didn't know that AOL even offered IMAP access...
What I would suggest doing is testing whether the SMTP server cannot be contacted on the port you are using, or whether it is reachable but producing some other sort of error. To test the former, the next time you get this error, try doing the following in your Terminal:
telnet smtpservername 25
If you are not getting a response, this is a networking issue, not a Mail issue. Chances are, the default port (25) is being blocked by the ISP you are with. Try the same telnet test but to port 587, and if that works, update your mail configuration to use port 587. This is the submission port, and an alternate port for sending mail - either unauthenticated or via TLS auth.