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

[Arnt Gulbrandsen <arnt@xxxxxxxx>]

Jeff Macdonald writes:
> Unless of course I am mis-understanding section 4.1.4. I'm not sure 
> how a sending MTA knows it is sending email to a relay. I'm assuming 
> all receiving MTAs could be a relay.

Not within the SMTP universe. The best-priority MX will do final 
delivery, whatever that means — I'd say it means the message crosses 
the border from where SMTP applies to somewhere else, such as where 
X.400 applies or where local policy applies.

Arnt