Does anyone know how to stop iOS from zooming when you double tap in an email?

I'm generaly against overiding the option to allow a user to zoom but, we're doing a lot with interactive stuff and users keep acidently zooming when clicking on stuff during our user testing.

This meta tag works in iOS safari but not in iOS mail

<meta name="viewport" content="width=device-width, maximum-scale=1, minimum-scale=1, user-scalable=no"/>

Any ideas?