A bit old posting, but as I guess I'm not the only one who has looked for this here is some info on the Kolab/Kroupware solution:
http://kolab.kroupware.org/
Kolab Server
Kolab is a secure, scalable and reliable groupware server.
Some of the major features include:
A web administration interface
A shared address book with provision for mailbox users as well as contacts
POP3 as well as IMAP4(rev1) access to mail
Some of the major components of Kolab Server are:
OpenLDAP
LDAP is used as the cornerstone for Kolab. All authentication, be it the web admin interface or POP3/IMAP mailbox access uses LDAP as the password store through SASL. Key configuration parameters are also stored in LDAP and automatically applied to configuration files after a change occurs. When you create a new user in LDAP, the Cyrus mailbox is automatically generated for you.
Postfix
The mail transfer agent (MTA) for Kolab server. Postfix is easy to configure and has a Sendmail compatibility interface for administrators who are familiar to Sendmail.
Cyrus IMAP
Cyrus provides IMAP as well as POP3 access to user mailboxes. It supports key features such as ACL (Access Control Lists) that allows more than one user to share mailboxes and folders and supports the Sieve mail processing language, this allows Auto Actions such as Auto-Forward and Auto-Reply on mailboxes. Cyrus is also highly scalable.
Apache
Apache is used for the web administration interface as well as to provide WEBDAV access to Free/Busy information for the mail clients. Soon Kolab will be using Apache and PHP to provide webmail access with groupware functionality.
ProFTPd
ProFTPd is used by legacy clients to upload Free/Busy information to the Kolab server
SASL
SASL (the Simple Authentication and Security Layer) is used by all the components and uses OpenLDAP as the store for Authentication information.
