[CentOS] Need help in securing maildir so that root user should not able to read anyother user's mail

Hi friends,

My company is currently using Exchange Servers for Mail Server
solutions but now they want to move to Linux Servers due to heavy cost
involved with the Exchange Users.We will be using the latest version
of Centos.

So the kind of solution we are looking is below:


a) Postfix or Sendmail as MTA.
b) Dovecot or Cyrus Imap with Quota as Pop & Imap server.
c) Security of Maildir means even root user should not be able to read
any user's mail.
d) Global Address Book on Ldap or any other.
e) Using samba/ldap for client authentication.

Most concerned part here is part c as we don't want any user to be
able to read any other user's mail including root.

Regards

Ankush