I've had some partial success although I still think I need to contact AOL and try to find a better solution than this.

I discovered that mail will send from my aol address, through AOL's smtp server, but fails when I try to send from any other email address. This means that while I can put whatever I want in the "reply to" field, the email appears to be sent from my aol address.

Not only is this confusing, but I don't actually want as many people to have my main ISP address, so that it stays relatively spam free. I can repoint aliases anywhere, but not my main aol email.

What's more, this never used to be the case and I can't understand why it's now happening. However at least it's progress of a kind!