Thank you for the excellent and detailed explanation.  Although I am
playing the role of the whiny and demanding user here, I do a
significant amount of development at my day job in Perl, SAS and other
environments.  I appreciate having these details in hand so I can
better understand the code when I can get around to learning it.
Although I have yet to "dive into Python," this project is giving me
another reason to do so.

Your explanation also helps me to understand better the issue with the
folder tree rebuilding and why hep's IMAP doesn't support flagging
messages.  Messages can't be modified if they aren't stored anywhere
on hep's server.  I think I was confused initially because, to me,
IMAP implies that I am managing resources dedicated to me on the
server.  I have now reoriented my view of hep toward a more "universal
translator" angle.  I'll have to look into yarn a bit to further
refine that understanding.

By all means, make sure you take the time to do things right.  It is
your duty to guard the integrity of hep's architecture, not to bow to
the whims of some crackpot user like myself.  If there is no place for
this sort of statefulness in your vision of hep, you should also make
that call, too.

In more practical terms, what this means for hep users in the near
future is that if they want to retain messages, they need to use the
POP interface or a modified IMAP reader that retains messages even
when they're "removed from the server."

Am I right in thinking that this also implies that if I'm not
"checking mail" via hep regularly and an RSS server such as Slashdot
"overwrites" the older messages in their feed I could be missing
messages?  I guess the way to get the behavior of other RSS readers,
in this case, would be to ensure my mail reader is set to retrieve via
POP every hour.

I'll have to experiment a bit to see if I can get the behavior I want
without hacking hep.  One thought is to configure an IMAP server of my
own (which I have been considering anyway) and use some scripts to
call up hep periodically to populate the server's folders.  One
advantage to this approach is that I could use an industrial-strength
IMAP implementation and my regular e-mail could sit in folders right
alongside RSS messages delivered by hep.