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

Jeff Macdonald wrote:
> 
> On Thu, 2008-07-24 at 18:34 +0100, Tony Finch wrote:
>> On Thu, 24 Jul 2008, Arnt Gulbrandsen wrote:
>>> Not within the SMTP universe. The best-priority MX will do final delivery,
>>> whatever that means
>> RFC 2821 defines "final delivery" and it has nothing to do with MXs. It
>> simply means delivery into a message store or some other non-SMTP system.
> 
> Ok, you both lost me. Or Perhaps you are agreeing with me. How does a
> sending MTA know that final delivery has happened?

it doesn't.  only the receiving MTA can know this.

Keith