People that own a pc which is on the route between you and the recieving AOL mailserver can read your plaintext mail.

i think the biggest danger is the LAN you are in. If this lan consists out of hub's or "lazy" switches youre mail can be red by all the machines on this local lan, it can be done quite easy with program's like Ethereal sniffer.

The machines out on the internet can also read youre mail but there will be lot's of traffic there so it's quite hard to pick out the right mails (if they know you and filter at you're ip adress they can retrieve youre mail!!)

Solution:

Use PGP Pretty Good Privacy to sign and encrypt your mail!