At 04:10 AM 1/16/2008 +0100, Frank Ellerman wrote:
Michael Deutschmann wrote:
The relay at the sender's border is called a "smarthost".
AFAIK a "smarthost" is what's today also known as "MSA":
A relay knowing what to do with mails going "elsewhere"
from the POV of the sender. Not necessarily the border
MTA talking with MXs "elsewhere". This nit can be very
important for SPF, just because you know all your MSAs
doesn't guarantee that you know all your border MTAs -
sometimes I use "mailout" for MSA != "mailout" setups.
-- MSA: Mail Submission Agent. An MTA that interacts directly with
users submitting mail, verifying their identity, providing secure
connections, etc.
-- MX: Mail eXchanger. Any MTA that has an MX record in DNS. The word
eXchanger suggests a bygone era when there was little spam, and MTA
functions were so simple that incoming and outgoing mail were both
handled by the same server.
I've been thinking of the MSA as just a part of the Transmitting Service, since
that is where Senders submit their mail, but it can certainly be split out in
discussions where that level of detail matters.
/
Sender(s) --> MSA/Transmitter --> / --> Receiver --> Forwarder(s) -->
/
Border
I can't think of any example where the MSA and Transmitter would be in separate
ADMDs. Crocker suggested that there was a need for "aggregation and routing"
to be handled by a separate service, but I wasn't able to get any clarification
of what he meant. I thought routing was handled at the Network Layer by
routers, and the Network requires small packets, not aggregation.
-- Network Layer: http://en.wikipedia.org/wiki/Network_layer
The relay at the recipient's border is called an "MX".
Yes, ignoring the address fallback if there's no MX for
the moment.
Also, the definition doesn't fit well with how we are trying to describe the
roles of the different Agents/Servers. An MX can be any MTA in our diagram.
Even an MSA will have an MX record, if Senders are expected to reach it from a
remote location.
-- Dave
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