Hi Talli,
a) We run IMP 3.1 with ACS 3.5 for over a year know, tightly integrated into a portlet.
b) Yes, not good enough for running an Intranet Webmail System for more than 10K users.
c) No, and never was. Integration is the way to go, especially as there are excellent systems out there. You might want to bother about having not the same look and feel, but seriously, users don't bother.
d) dunno
e) I'd request nothing that can be handled better by third party applications. This means, leave IMAP, Sendmail and POP server out of the Scope. Take a look at IMP or Squirrelmail. Look at fastmail.fm for enhanced features. <sarcasm>Take a lot of work and even more time to reprogramm theses things in OpenACS and start wondering afterwards, why you did it.</sarcasm>
Sorry to be sarcastic here, but the problem has come up a multiple times and so far nothing has come up, for a very good reason. Creating a good webmail system is complex and takes a lot of effort. Effort, this community should not try to put it's resources into at the moment. Interfacing the basics of a webmail system is easy, relatively speaking. People don't bother switching to a different system. They don't even bother to have to signone twice (though we try to get around this). As long as it works, is untuitive to use and looks sleek, they are happy. At least our experience so far.
That said, setting up IMP, Cyrus, CyrusSASL, Postfix, OpenLDAP and integration into AOLserver is a PITA. One we did not even bother to write a documentation for so far (otherwise I'd have said right in the beginning, here is the URL, that's how we did it, go figure out for yourself). Once we have it, I'll announce, how long will it take, I don't know. How long will it take an average person to setup: 3 days. Maybe more. Or less, if you start without RPM's, take bleeding edge software and pray it works together.
LDAP is a crucial part into integration in general, though you can play around it for sure (or keep databases in sync as we do with Jabber). Therefore we look forward to Collaboraid's effort in this matter, as it will allow us to integrate even more different systems that clients happen to use (Next on our target list is Lotus Notes, probably).
