You can go into settings and find the data usage section. From there you can go, app by app, and disable background data. This lets you pick and choose what apps will load in the background and which one are blocked from doing that.
This is a tough question to answer because you are asking two different things. One, you are asking to stop apps from updating. My peers above have answered that and it will take some work to manually go through each app. BUT, you've also mentioned that you want to use email only. Now that means that you want internet connection BUT you only want it for email only. For that to happen, you would have to get rid of all your apps! That's the only way to ensure that no other apps are using data other than you email apps. This is a little extreme of course. But if you have, say, a smaller data package, you must be sure to always have your data turned off and use wifi. This will ensure control over your usage.