In addition to restricting which clients can synchronize with which tenants, you can also limit what type of file type (based on the file extension) can be synchronized with OneDrive. To configure this setting, follow these steps:

1. Navigate to the OneDrive for Business Admin Center (https://admin.onedrive.com) and select Sync.
2. Select the Block syncing of specific file types checkbox.
3. Enter the file types to block from synchronization, one per line, as shown in the following screenshot:

4. Click Save.

OneDrive for Business client computers will be unable to synchronize files with extensions matching the listed file types. During the next synchronization cycle, if the OneDrive sync client detects files whose extensions are blocked, you will see the following notification error:

Additionally, if you open the OneDrive sync client in the system tray and view the errors, you will see that the client is reporting the name or type of file that isn't permitted:

Renaming the blocked files will allow them to be synchronized successfully.