You can put the unused apps to sleep. There are settings which put unused apps to sleep. And, if you don't want certain pre-installed apps to function at all, you can go to the APPS section of the settings and disable them if you can't uninstall them. But, seriously, tap on the RECENT APPS (III) button on the bottom of the phone and you can see all the apps you just opened or previously opened. This allows you to return to any one of them that are open if you are multitasking between different apps. But, every app still left open bogs your processor down more. When you are finished with them you can swipe away the ones you are done with, leaving the ones you're still using. But, if you're done with all those apps still running in the process you can tap the CLOSE ALL button and close them all. And, it also helps to clear history and close all previous tabs in your browsers too. This also helps reduce lag. Also, recommend a reliable app to clear cashe files and clean your RAM memory. This also helps.
My email app is starting and running in the background. I know how to close apps and the othercthings you described. I want to stop the email app from starting and running in the background.
Putting apps in deep sleep closes all background data entirely, so if you use the email app, you won't get notifications sent. You can also hard press email app >click info > click on both mobile data or battery and toggle off background use. Deep sleep is the better option though.
