the topic was already raised in 2013 by explanoit ( https://forums.manageengine.com/topic/sign-notification-emails-s-mime).

Regarding to your employee Raghuraman Balaraman this feature was planed to be implemented in "future releases". Now we have almost 2017...

Can you give me an estimation when this very important feature will be available?

Thx in advance my friends!

With best greetings from Germany

Alex