How to add S/MIME certificate to samsungs native email app on galaxy s3
After a long time of researching I found this useful link:

http://www.gridshore.nl/2013/09/30/setting-up-keys-to-sign-emails-in-samsungs-android-email-app/

It seems to be the case that it is not trivial to make android to find the keys. You need to place them in a special folder with a special filename. 

But the worst is that samsungs email client supports S/MIME only for exchange connections and not for pop3 or imap. I cannot imagine why this is the case but it seems to be true.

All of that makes me belive that some people dont want us to encrypt or sign our emails. What a shame!