would like to use S/MIME on ipads with gmail

Hello, my wife and I would like to be able to send and receive encrypted emails. We both use Gmail. I tried importing the certs into our ipads. however when i type in my wife's email address I get a cert can not be found on the server. I'm assuming that the ipad is trying to find the certs on googles server. Is there a way that we can use this feature using our gmails accounts? Any help will be most welcome.