If you attempt to force procedures down users throats without having made their lives easier (and no, vague promises of it being better for someone later doesn't count) then they will rightly see you as a roadblock to route around.

The result?

A bunch of pissed off users who will find the quickest way through the roadblock. If that is to say that all mail is personal, they will do that. If that is to create a single "project" that they file everything under, they will do that instead. If you don't have your users on your side, you will get garbage in.

Therefore my suggestion is that you do what you can to make it as easy as possible to voluntarily comply. You also make sure there is an obvious user value, and let everyone know the benefit. And finally prepare an internal reporting tool to monitor who is using the system and target your requests appropriately. (Also solicit feedback.)

This may seem like a lot more work than forcing people to live within your dictates. But unlike forcing peope to live within your dictates, it has a chance of working, and a chance of getting through without leaving everyone hating you as public enemy number 1. And if you do force people like this, well don't do as some people do and go complaining about "lusers" because you will have only yourself to blame.

To summarize, forcing people to jump hoops is a guaranteed failure that will leave people reminded of a bad Dilbert episode. Therefore if you cannot find a way to get active and voluntary user cooperation, this project is a lost cause and it is a waste of time to go farther down this path.

(Sorry to sound so harsh.)