John White wrote:
>On Fri, Jul 21, 2000 at 10:30:41AM -0400, Mark Mentovai wrote:
>> That's very easy on a host-by-host basis, and I use it for certain setups.
>> The problem is that there shouldn't be any "domain in question," an MTA
>> should make efficient use of a limited number of SMTP sessions when
>> transferring mail to any other MTA.
>
>Why?
>
>I'm not trying to be too much of a smartass here, but you're
>projecting your ideas about nice network usage onto the
>smtp protocol, which doesn't demand it.
Why not? You can have your cake and eat it too. Efficient network
utilization doesn't mean delayed or slow delivery.
>How is this accumulation supposed to occur? Per queue injection?
>Over a time period? How long of a time period? As long as we're
>being good neighbors, should the mta lookup the mx for each
>recipient and accumulate by mx? What should we do if the dns
>gives us a 0 ttl for the mx?
None of the above. Let me give a loose description of what my idea of an
efficient and fast MTA can do:
When an MTA receives a message that should be sent out remotely, it should
determine, in order of preference, which remote hosts are candidates for
relaying the message. It should then attempt delivery to the
best-preference host it can find, unless a certain number of active SMTP
sessions to that host are already open. (This number can be one, or it can
be something else small in the interests of allowing for parallel delivery.
It should not be unlimited.) If there are already too many active SMTP
sessions to the remote host, the message should wait until one of those
sessions has finished transferring a message. Instead of closing the SMTP
session, the sender would then transfer the new, waiting message. When a
new message hits the queue and a delivery is attempted, any other messages
in the queue waiting to be delivered to the same host should also be sent
across the same session, or set of sessions.
An MTA should not split the same message up into multiple messages when
transferring them beyond reason. Although RFC 821 recommends that an SMTP
server implementation place no arbitrary limitation on the number of
recipients per message, it mandates that mail servers must be able to
process up to 100 recipients. If an MTA receives a message with 100
recipients with the same MX, there is no reason to transfer the message to
the remote mail exchanger 100 times.
Mark
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Mark Mentovai
UNIX Engineer
Gillette Global Network
