Even though it is possible to search mail at the moment, it is not convenient or granular enough. You are still required to subsequently scope your search to mail objects and then you don't have the option to specify the sender or subjects.

It would make the archive page more usable if there was a filter on that page to allow filtering on subject and sender as in most mail clients to manage the sheer bulk of mail. If searching on the body of emails, the search box from the mail archive page should redirect back to the main search page, but it should automatically scope the search to mail objects only.