DavMail Calendar support is now available, tested with Thunderbird/Lightning and Apple iCal. This should also work with other Caldav clients.
Obviously, you need to install the Thunderbird Lightning extension. You can then create a new network calendar:
Choose CalDav format and specify location (adjust port to your settings):http://localhost:firstname.lastname@example.org/calendar
Replace email@example.com with actual user email address.
Choose a name, color and set the associated email address (as set in mail setup).
Note that Caldav notifications will not work if this email address field is empty.
Provide your credentials, login is Active Directory account name, i.e. domain\account or email address with Exchange 2007
You may want to enable the (experimental) Lightning calendar cache feature to avoid the possibly long calendar load task delay on Thunderbird startup: double click on the calendar in Lightning left pane and activate cache. Restart Thunderbird.
Proceed to Thunderbird directory setup