AOL, was Yahoo and their mail filters..

[johnl at iecc.com (John R. Levine)]

> 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 at 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.