> Do you agree with  this analysis, and what would you  decide about sending the
> notification to the sender or not?
>
>   Eric
 
I think sending to both sender and receiver is the best thing to do.
 
Isn't there a convention for interactive messages that messages
generated by a server begin with an asterisk (e.g., *GONE ...)?
Couldn't that same convention be adopted for mail (i.e., first
character in the subject would be asterisk) so that server machines
would be better able to dispose of mail generated by other servers?
Another way to do it would be to invent yet another header type.
 
Any way it certainly would be nice to have a well-defined way of
preventing dueling server machines from exchanging messages forever.