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

2008-07-25 03:32:57

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.

If you've delivered to the best MX, then that's as far as SMTP takes the message. The message may have a long way to go, but that's independent of SMTP and DELIVERBY. For example, the recipient may use something like Thunderbird offline, in which case the recipient's inbox at the server is just another spool, emptied when the recipient polls.

The recipient's SMTP server won't know that, 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.