I run Andriod 4.3 (9.2.A.0.295) on a Sony Xperia V.
There is support to use S/MIME encryption in the native email client, you can use the security settings for each email account.

However, I am not able to install my S/MIME certificate, the system says that it cannot find my .pfx file?
It says that it should be on the external storage, but its till cannot find it. Any tips on how I can accomplish this?