With encrypted indexes maintained on the client end. Web search is a complex problem, but searching a single user's mailbox is child's play, you don't need Goog

With encrypted indexes maintained on the client end. Web search is a complex problem, but searching a single user's mailbox is child's play, you don't need Google for that. Client end processing could work for advertising too, but at that point you have an information leak that severely weakens security, the client will ask for adds relevant to terms found in the message.