🚀 go-pugleaf

>The AT&T packages that are more or less "on-line" and able to send at any
>time generate the receipt when the message is displayed on the screen
>(that is, the user selects "read").  The dial-up versions (access-plus
>and the windows and mac equivalents) generate the receipts as the messages
>are transferred out to the remote machine since they will be off-line
>as they are read.  The wording of the receipt is different to indicate
>the condition.

A friend of mine once wrote a popular (well, at least in the local
UUCP net of our employer) mail user agent which attempted to implement
read-mail-receipts, using Return-Receipt-To:.  

Various refinements occurred.  One social problem which happened 
rapidly was the use of the mailer to send mail from A to B and C with 
return receipts to D, E, F, G, and H, the return receipts being an 
intentional form of harassment.  It initially wasn't obvious to the
victims that A was the one doing the harassing.  A bug that got fixed 
pretty fast was that the "Return-Receipt-To:" header somehow wound up 
in the receipts, causing infinite receipt loops.  Various refinements 
were needed to the algorithm needed to determine "read", and eventually
the receipts started saying "read your message", "saved your message
to a file", "deleted your message without reading it", etc.  Some
people considered this an invasion of privacy (although many of
them didn't mind the original design).  Some of them discovered
how to provoke the mailer into issuing more than one receipt for 
the same piece of mail, and did so, frequently.  Someone who went
on vacation for a week was likely to end up with a megabyte of
receipts in his mailbox, even if he never sent a piece of mail
asking for a receipt.  The use of "more /usr/spool/mail/$USER" as
a mail reader increased greatly.

A big problem showed up when I used the mailer to examine a very large
file of archived mail, and it started sending receipts to all of
the hundreds of year-old-and-older messages.

Please try to design return receipts in a way that can't be used as
a weapon.

					Gordon L. Burditt
					sneaky.lonestar.org!gordon