AOL's ARF redaction also causes problems identifying problem .forwarders. I don't understand what they are trying to defend against.
Oh, I went around with them a few times and finally got a reasonable explanation. They're concerned about disclosing the recipient of a message to someone who didn't send it. That's why they redact the recipient address, but not an ever-so-lightly encoded version of it elsewhere in the headers. If you can decode it, you presumably must have put it there in the first place. They've redacted more heavily than that in the past, but it turns out that was buggy software, not policy. So if it's a problem, just add and X-forwarded-for header with a rot13 version of the address and you can always recover that. I also gather that if you happen to have run your mail through a filter and have an opinion of its spamminess, an X-Spam-Status header is treated as a hint to deliver to the spam folder where it won't counted against you, but it's still there for the user in case you guessed wrong. Regards, John Levine, johnl@iecc.com, Primary Perpetrator of "The Internet for Dummies", Information Superhighwayman wanna-be, http://www.johnlevine.com, ex-Mayor "More Wiener schnitzel, please", said Tom, revealingly.