Re: MS vs. pop and imap

Dave,

One observation...

While I tend to agree with Ned that looking at the history is 
not particularly useful, I suggest that your summary of the 
history is not correct either (it certainly isn't consistent 
with my recollections).   In the stage before the idea of a 
Message Store was more or less explicitly slid into the 
architecture and we still spoke of an MTA handing off a message 
to an MUA, POP and IMAP were usually described as "split-UA" 
arrangements.  I.e., with "traditional" access mechanisms, the 
UA had a user-facing component and a component that pulled the 
message from wherever (or in whatever state) the MTA had 
delivered it.   With POP and IMAP, that MUA was divided into two 
parts, one that co-existed on the same host with the MTA's 
delivery mechanism and served out data to the the other one. 
The latter sat on a client machine and requested and/or received 
and/or accepted those data.
Now, even with the introduction of Mail Delivery Agents and 
Message Stores, that "split-UA" model may still be somewhat 
useful.  I note that we don't make any attempt to distinguish 
among single-component MTAs (of the emacs rmail command, or the 
bin/mail variety, or up the complexity scale from it) depending 
on whether they facilitate leaving messages in the mail store 
after reading or require either deleting them or moving them 
somewhere and that, similarly, we don't make distinctions based 
on whether those MUAs can modify the stored message with 
annotations, "answered" flags, etc.  I think that, if one tries 
to contend that POP and IMAP are different sorts of beasts, then 
one needs to start reclassifying the MUAs that don't involve 
client-server splits, and that would get us quickly into a silly 
state.
Using similar logic, I think I'd join others in discouraging 
hair-splitting about what is and is not a legitimate mail store. 
The reality is that we have fairly few firm boundaries in this 
business (as someone, I think Ned, pointed out, the concept of 
"final delivery" is one of them, even if one wants to quibble 
about whether it should have been called "final") and that the 
sort of model you are trying to develop is probably best seen as 
descriptive, rather than normative.  If you try to make it 
normative, I think there are big problems ahead.
best,
  john