Required domains for whitelisting Dropbox

I have clients using Dropbox, and while it does autoload the proxy setting, and this seems to work, I need to whitelist the sites required.  At the moment, I have a list that started with *.dropbox.com, and grew by adding denied sites that "looked like dropbox" around the time a user tries accessing the service.  But it doesn't seem to be enough.

Is there a list of URLs/FQDNs that need permitting to make dropbox work?  I could not find anything on this on the support pages.