Storage available to end-users is defined by Storage quota and Overage.
Storage quota is the amount of space provided to a EUC or an account in a EUC for storing backups. If this value is exceeded, the group administrator and the administrators of the parent group will receive an email notification. Backups will continue until overage is reached.
Overage is the amount of extra space provided to a EUC or an account in a EUC for storing backups while actions to inform end-users about exceeding storage quota, arrange payments and/or enlarge storage quota can be taken. When the overage is exceeded, the end-user, the group administrator and the administrators of the parent group will receive an email notifications (once a day). The first backup that exceeds the overage will complete successfully, subsequent backups will fail.
Overage quota is available starting with version 4.2 (Agent build 12.0.1588). To enable this feature, update all Agents to the latest build. See this article for help.
To set up or change a storage quota or an overage quota see this article.
Number of machines that can be protected is defined by Physical workstations, Physical servers, and, starting with version 6.0 (server version 6.0.521 or later), Virtual machines, Mobile Devices quotas and overage. When the quota is exceeded, a notification is sent. When the overage is exceeded, end users will not be able to protect more machines of this type. If a quota is set to 0, end users will not be able to download the installation package for this type of machines and will not be able to protect them.
To set up or change machines quotas or overage see this article.