To migrate the user data off, you need to have the users store the info in
local .pst files. There is a tool that will go through and do this for all
the users, saving the individual .pst files on the server. This will also
grab all of there calendering, notes, etc. info as well. The name of the
tool escapes me, however it is in the M$ Exchange Resource Kit.


I just read an article about setting up a reliable email system based on
Linux, however I have slept since reading it...maybe Sys Admin or Unix
Review or one of the BSD sites.

Anyway it looks something along the lines of this:



          Server1
      forward server
             |
             |
   _________________
   |                |
 Server2         Server3
  email            email
   |                |
   ------------------
            |
         Server4
         OpenLDAP

You should be able to have OpenLDAP 7 MS Active Directory talk to each
other, but I have not done this personally (yet!).

Hope that helps.