he search query for all unread threads is:
/gmail?search=query&q=is%3Aunread&view=tl&start=0&init=1&zx=
The main parameters are search= and q=, which define what set of threads the user is requesting. The zx= parameter is a proxy cache defeater, and I've omitted it here for brevity. See GmailAdapter.MakeUniqueUrl() for more information.