The TonicDM Outlook add-in can be pushed to staff based on groups using the Centralized Deployment feature in the Office 365 admin center.
When logged in as an Office 365 Admin:
Navigate to the Admin Center in Office 365.
Click Settings — Integrated Apps — Add-ins — Deploy Add-In.
Enter the URL of the manifest: https://tonicdm.com/outlook/office365.xml
Be sure to include the https:// even though the field indicates you don't need it!
Select who should have access. We recommend choosing Everyone at least until you know the deployment is working.
Note: historically nested groups have not worked: the users must be members of the top-level group.
For Deployment Method select whether the add-in should be mandatory or optional. Optional would allow staff to remove the add-in from their Outlook. We recommend choosing Fixed.
The add-in will not appear immediately. We've found that it takes several hours for the add-in to appear in the Web version of Outlook (outlook.office.com) and between several hours and several days to appear in the installed version of Outlook.
The add-in will now be listed in the Office 365 Admin Center. This is where you can modify settings, for example which staff the add-in is being deployed to.
Microsoft's full instructions for deploying add-ins is here: