Rasa is pretty much right on. The error you are getting means that your mail server tried to send the mail to the AOL box three times and it never made it.
There are a couple of reasons that this happens but it is usually due to network traffic. Most of the time AOL is not at fault. Possible causes are that the network becomes over loaded and things time out, backbone providers hose routing tables or some schmuck with a backhoe cuts some fiber. I worked at AOL in the NOC and saw all these things, and more*, happen.
AOL gets pointed out when these things happen because AOL is the biggest provider out there. Since AOL is the biggest, and by a huge margin, you hear more complaints about AOL.
** Derleth**,
While you may hate the AOL client you can do everything on AOL that you can do with any other ISP. Also just in case you didn’t know, and you didn’t, AOL uses MSIE as the browser not Netscape. At the same time AOL released the Netscape code as open source and Mozilla(the open source version of Netscape) is tied with Opera as the best browser out there.
At the same time AOL has the biggest and baddest backend in the world. AOL has more people online during peak periods than most ISPs total user base.
Slee