Is there a way for Zimbra to automatically create new e-mail accounts based on linked Active Directory accounts?

I'd ideally like to set up authentication in such a way that I can create new users in Active Directory (under "mydomain"), and automatically be able to log into that user's e-mail account without having to separately create the user's e-mail account in Zimbra (newuser@mydomain.com). Is this doable?

I've got Zimbra v6.0.13 running on Ubuntu 8.04 and Active Directory running on Windows Server 2003 on a separate network.