I know it seems like I jump on a lot of bandwagons (I hate Microsoft, I hate AOL, etc), but there is a reason these companies attract a lot of vitriol. They try to be all things to all people, and they want to do it their way, not our way. As a result, they tend to make things difficult.
Case in point. A client had a spam filter in place on their main email server. The secondary email server (which had an MX record with a much lower priority) was set up to accept messages from only the primary server. So, when AOL decided to send emails to this client, which email server did it try 90% of the time? The secondary server. Which, of course, caused bounce back messages. And, since I cannot force people to give up a dead horse (“I’m sure the horse is just resting and I will get to my favorite place any time now”), I had to open up the secondary server to accept from all….for now. As soon as I can get a definitive list of AOL mail servers, the chastity belt goes back on!