users - imap client, browsers
/ \ / \ / Authentication \ Server 1 \ Server 2 Postfix (SASL, TLS) <--> Courier IMAP (TLS) <--> Samba/LDAP (SASL, TLS) SquirrelMail (https) <-->
This is more or less what I implement. *But* not with the luser 2.0.27 you suggested, Postfix is snapshot, LDAP is 2.1.23, Cyrus SASL is 2.1.15, Courier is 2.1.2 and Samba is 3. You don't need NFS, just processor and storage.
How to do it? Each component has to be learned individually and in combination with each other one. In addition, there is PHP4 for web applications, etc. And Postfix 2 could just have well been Exim 4, I can do both. There is no short cut possible. Use the mailing lists to see what people say about setting your stuff up, but do not ask for help until you have tried everything you can possibly do to make things work on your own. Then you should hardly ever need to ask for help. Always use the very latest, acknowledged bug-free source and compile your own. Make your own rpms, debs, pkgs, whatever, if you wish and do not rely on others', second-hand packages. Pray to God that your "Management" has enough sense to give you the time you need - it will probably run into many months.
I appreciate the insight Tony.
Cheers,