There are actually two methods that work. The most reliable option is to go to www.aol.com and sign on to web mail. It's your same account, and if you keep the mail you read there as new, you can still store tham as you normally would using your regular mailbox later.
They also say that if you make sure to add no rich elements to your mail (color, links, etc) set it on Arial, size ten, it will send plain-text only. I'm not going to trust it.
More information is available from AOL's mail FAQ.