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Re: MS vs. pop and imap

2004-05-31 09:37:59


CD>            |        MTA
CD>            |         |
CD>            |         |  smtp, lmtp
CD>            |         |
CD>            |    +-- MDA   <-------------------------+
CD>            |    |    |                              |
CD>            |    |    |  smtp, imap, (local)         |
CD>            |    |    |                              |
CD>            |  smtp   MS                           sieve
CD>            |    |    |                              |
CD>            |    |    |  imap, pop, http, (local)    |
CD>            |    |    |                              |
CD>            |    +--->+                              |
CD>            |         |                              |
CD>            |         |                              |
CD>            +------> MUA recipient (rMUA) -----------+

Your diagram implies scenarios such as delivering into the MS by imap
and then having the MUA access the MUA by pop. Do we really want to
imply that?

We need to get clear about the difference between an MTA-related
transfer of responsibility, versus an action with the MUA of moving a
message from one folder to another. In the former, the message is held
in something that is a queue. It's difficult to imagine any utility in
modeling a folder as a queue.

CD> - some clients 'pull' messages into their local store via smtp and ETRN,
CD> bypassing the message store.

For the scenario you describe, what is the difference between a Message
Store and an MTA's queue? It suggests that "delivery" is bypassing the
MS. I don't know what it means to bypass the MS. Where does the message
go? Onto the MUA's screen?

CD> - I'm afraid we cannot ignore webmail, so note the addition of http as an 
MS->>MUA access protocol. I guess http should appear for the sender MUA -> 
CD> MSA step in which case the MSA is actually a webserver.

2. HTTP is not used to deliver, post or even transfer mail, as a
semantic object. It is used as a front-end exchange protocol between an
application and the user interface (the display functions.) It has no
semantics for the data being transferred. So the use of http is really
within a split MUA. (Hmmm. Maybe that's the elaboration that will help,
showing a cross-net split MUA sometimes and not others?)

In other words, http is a presentation-layer exchange protocol, not an
email protocol.

So it is really more like telnet than smtp, pop or imap.

webmail is an important data point in an array of marketing
distinctions, but I do not see how it warrants reference in an
architecture discussion.

 Dave Crocker <mailto:dcrocker(_at_)brandenburg(_dot_)com>
 Brandenburg InternetWorking <>
 Sunnyvale, CA  USA <tel:+1.408.246.8253>, <fax:+1.866.358.5301>