Re: Intent to revive "expires" header from draft-ietf-mailext-new-fields-15

Chris Haynes wrote:

[ a bunch of stuff with which I agree, followed by: ]

> In my view:
> 
> 1) To introduce the Expires header with a semantic which permits the mail system to silently discard messages (wherever the message is at that time) would be bad requirements engineering,
> 
> 2) The only possible role for such a header would be as a 'hint' to recipients, who may opt to give their user agent permission to delete messages (probably selectively - based on sender, topic, etc). But such a 'hint' (and its implementation) should not be discussed and defined at the 822 architectural layer - it does not belong here.
> 
> So, FWIW, I think it is a bad idea to consider it in an 822 forum - whatever semantic is attached to it.

I think it's rather odd that people are arguing that a proposed 
extension to the 822 (i.e. user-to-user) protocol can only be used by 
what is arguably mail transport (or on the boundary between transport 
and the recipient's user agent).  It certainly doesn't belong in SMTP. 
Nor does it belong in a body part, since it's clearly a message-level 
function.

Where else can we put it?