Email apk to install in another androind version

Hello All,

I like the version of mail that comes with Sprint/Samsung 5.0.1, I made a backup of the application (apk) and put it onto an SD card.
I then under my different version ROM ( Samsung/GS6 ROM I Beleive it's 5.1.1 ) tried to install it, however it doesn't let me.
Is there a magic thing I'm suppsed to do either on the backup or installation part in order to install that on my current rom?
Any suggestions or reference material?

Thanks!!