AOL is lots worse than your indications suggest....
Last year, I found that my home SMTP server was being "hung up on" by AOL's mail server. No SMTP error would be returned. The text of the logged session ran off so that my server couldn't log it all. I had to actually TELNET to AOL on port 25, and manually start sending mail (yep, se habla SMTP ... with RFC821 in my lap) to read their entire blurb stating, basically, that my "residential IP" (on Time-Warner) was blocked. The session was then closed on their end. Very rude, and not very SMTP-friendly.
It gets worse. I started getting bounces from AOL from e-mail relayed from my domain server (other than DreamHost, at the time). A basic 550 or 554 error, but misused by AOL IMHO. I had to go to their page to find out that they bounced the message based on a URL in teh content ("What," I said, "you're searching the text of private email and bouncing based on what YOU think is objectionable?! !&%^#*"). The URL that they claimed was a source of complaints? TextAmerica.com. A photo blog site. Not a spammer. I complained to both TA and AOL, and neither has done diddly about it.
So (moral of the story) be forewarned when you get these brief 554 errors, follow the trail to the bouncer's web link and find out what they're REALLY doing. In AOL's case, they're just bouncing e-mail not due to technical concerns, but censorship activity on their side. Basically just shutting out huge swaths of the Internet on spurious criteria. Quite ironic considering their rash actions in 1994. I think this kind of #&@* literally "breaks" the Internet (as designed) and encourage all my contacts to ditch AOL as a mail provider.