You can setup quota threshold alerts at group level in UM 6.4, 7,x. From UM main page, navigate to Administration. Under the Threshold tab, change details of Qtree Quota as per your threshold requirements. Please note that this is global setting like 5.x, if you are to override global setting for a specific volume, you will need to navigate to specific volume and change the settings there.
Once you are done configuring the threshols, you can navigate to Administration --> Manage Alerts under the UM main page, and then setup quota level alerts by selecting:
1. Qtree as the resource (select all qtrees)
2. Select the requisite events associated to qtree thresholds.