You may have some users that you want to prevent from using gmail or other google apps- Heres how to achieve it.
1- Sign into your google admin area at admin.google.com
2- Click Users then click 'Manage Organisational Units' at the bottom of the page
3- Create a new Organisation under the top level domain.
4- Now navigate back to the google dashboard and select Apps>google apps> then click gmail
5- Choose the domain that you want to switch the apps on/off for and switch mail off for the new organisation
Now mail is switched off for the new organisation
6- Go to users and move the users into the new organisation where mail is switched off. The user/s can no longer use gmail