Hmm. Your MX record should point to the public ip address of your email server so that people/servers that send you mail will be able to find out where it needs to go by doing a lookup on your domain name (which should be transparent to the user sending you mail). But I don't see how that would stop you from sending mail out; it is related to getting mail in. As for why it won't send to aol at all, are you getting any nondelivery reports from the server? Those may help in troubleshooting why aol is not accepting the mail....
We'll work this out
/JD