[Dovecot] What's the best way to authenticate against Active Directory?

[Chris Johnson]

Hi all,
        I'm working on a replacement for a legacy linux mail server: courier POP/IMAP, Postfix, OpenLDAP. One of the requirements of the new mail server is to authenticate against our AD infrastructure (I'll still keep a userdb in OpenLDAP). SSO is not required since most of the clients don't log into our domain. The current system has about 1,000 concurrent users on it during the day (almost all are IMAP users). Inbox size varies but is generally very high 1GB+.

        I'm considering dovecot as a replacement for courier IMAP on the new server mainly for performance reasons. Cyrus was also considered but I'd rather work with maildir format inboxes.

I'm in the process of installing a "proof of concept" server with CentOS 5 and dovecot-1.0-1.2.rc15.el5. the production system will most likely run on RHEL

Question:
What's the best way (most reliable/fastest) to authenticate dovecot to AD?
If someone is doing this in a production environment can you offer any hints on configuration for performance or what to expect in general?

Thanks,
chrisj