@Tom: I think you may be able to enable/install the WebDAV role services, then disable them for just the SmarterMail site potentially. While we do both use WebDAV, I think the base IIS services and the SmarterMail DAV services might be conflicting. Can you check to see if this is a possibility?
Kyle Kerst
Lead Internal Network/System Administrator
SmarterTools Inc.
smartertools.com