Robert A. Rosenberg <[EMAIL PROTECTED]> wrote: > At 18:00 -0400 on 04/30/2008, John Leslie wrote about Re: Queued Mail > or Unreturnable Mail?: > >> We certainly could design a mechanism _better_ than MX records to >> document intent relative to receiving email, especially DSNs. But unless >> and until we do, folks are likely to use MX records as part of the >> balancing act of guessing the probability of NDNs reaching a responsible >> reader. > > IMO: The publication of a MX is a statement to "Send [EMAIL PROTECTED] > Addressed > Email HERE". Once an SMTP Server does so and delivers a NDN message > addressed to [EMAIL PROTECTED] to the MX, it has done its job and turned over > Delivery Responsibility to a MX designated Server. The fact that the > MX Server (or one that it forwards the NDN message to) then turns > around and sends is to /dev/null is not my SMTP Server's Problem > since, as noted, it did its job by delivering the message to the > Domain Designated injection point and turning over further delivery > processing to the Domain's Mail System. > > Thus the existence of the MX places the responsibility of "reaching a > responsible reader" on the MX not the Sending SMTP Server with NO > GUESSING involved.
An excellent point. The MTA generating a DSN has no obligation to guess the probability of that DSN reaching a responsible reader if there is an MX record for the domain in question. If that MX directs it to /dev/null, there's nothing the sending MTA could have done to increase its chances. Conversely, if there _is_ no MX, it's a pure guessing game. Will a particular IP address gleaned from a A)ddress record answer on port 25 at all? If it doesn't answer now, might it answer an hour from now? Might a different IP address gleaned from the same A)ddress query give better odds? If we finally get a SMTP session, but get "no such account", would it help to try a different IP address? My personal inclination is to declare "guessing" out of scope for returning DSNs. We already know that not every domain wants them. Declaring that one MUST send them even when the receiving domain has not expressed an interest in receiving them leads to known problems _today_. It would be good, IMHO, to have a clear way to declare an interest in receiving them, or _not_ receiving them, and recognize that in the absence of such a declaration, some MTA administrators will choose to send them, while others won't. -- John Leslie <[EMAIL PROTECTED]>
