So therefore, your article could have been titled "{Mailbox|GMail|iMail|all_other_mail_clients_ever} is a Security Fail!"?
Because as far as I am aware, few mail clients either support or (if they do) actively encourage an extra password layer, and your users do not want it. Given an average un-password-protected phone, you will be able to read their email even if they were using the iOS encrypted files framework, just by opening the app.
I apologize, but it appears that your headline is deliberate sensationalism. If you want to have a discussion about how we need to secure email apps in general, I'm interested. If you want to just pick the latest 'big thing' and take pot shots at it, nah.