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RE: Proposed change for RFC0974

1998-11-05 16:53:34
At 1:57 PM -0800 11/5/98, Doug Strauss (Exchange) wrote:

There are other conditions to think about with this logic.
        1.  The host which has the mail queued for delivery is obviously in
the MX list.
        2.  Delivery to MX records should exclude all MX records of equal or
greater values.

Thus if the config is correct, you would only be trying to deliver to the
lowest MX record which is either closer to the final host or is the static
IP of the final destination.

Assuming you are following this it should solve the problem you state does
it not?

My understanding of Albert's message is this:

1. A number of domains are set up with their own, intermittently-connected mail server as the lowest-preference MX, and their ISP (with a full-time connection) as the next MX.

2. Random sites trying to send mail might use an SMTP server which, in compliance with the MUST of 974, only attempts to contact the lowest-preference MX, which is not likely to be connected.

Note that 821bis, in "5. Address Resolution and Mail Handling" says:

To provide reliable mail transmission, the
SMTP client MUST be able to try (and retry) each of the relevant addresses
in this list in order, until a delivery attempt succeeds. However, there
MAY also be a configurable limit on the number of alternate addresses that
can be tried.  In any case, a host SHOULD try at least two addresses.

Which I think addresses Albert's concern.

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