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

On Fri, 25 Jul 2008, Arnt Gulbrandsen wrote:
> Jeff Macdonald writes:
> >
> > Ok, you both lost me. Or Perhaps you are agreeing with me. How does a
> > sending MTA know that final delivery has happened?
>
> It only knows that final delivery will happen, not that it has happened.

Final delivery won't happen if the message later gets bounced.

> If you've delivered to the best MX, then that's as far as SMTP takes the
> message.

SMTP can take it further if the message is relayed to an internal MTA
using non-MX routeing, and/or if the recipient address is forwarded
(aliased) somewhere else.

> The recipient's SMTP server won't know [what happens after final
> delivery], won't be able to control or prevent it. Since that's true
> even if it advertises DELIVERBY, I think it's acceptable to deliver to
> the best MX in R mode.

Yes, and the same goes for internal relaying and alias-forwarding.

Tony.
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