Access to User application can be temporarily suspended on a need basis. When suspend all access is enabled during server maintenance, users will be prevented from accessing the application.
Here are the steps.
Login to Admin Console and click on Settings from the left menu and then on Suspend All Access.
Click on Edit to make the changes.
By enabling this, the access to user application is temporarily suspended.
After suspending the access and saving it, when users try to access the user application, it will re-direct them to an access denied page.
Please note that access to Admin Console is not blocked.