iOS - S/MIME switch in Advanced Mails Settings should be posible to switch on/off. Actually blocked by installation of Exchange-ActiveSync.
If the switch isn`t blocked strictly by policy, user could choose if they want to sign, encrypt or something else by there self.
Stefan H commented
This Feature and the possibility to set the follow String in the Profiles.
With this setting a user could switch between encryption on and off
William de Vos - IMPROVES B.V. commented
Please make this possible