Block synchronisation of specific file types (OST files)
You can prevent users from uploading specific file types when they synchronise their OneDrive files.
OneDrive admin centre
Browseto https://admin.onedrive.com - Press Sync, and block the desired file extensions in this format:
Ost = Outlook ofline folder
PST = Outlook data file
PKG = a mac installation file
iso = an image file for Windows, for example.
The result is that OSTs will no longer end up on users' personal OneDrives.
This solves 2 problems: Long synchronisation times due to large files. And prevents forwarding of these files.
In this view, you can see clearly which types of files are not allowed.
This view shows where the 'problem' file is located.
After deletion you will see that there are no more errors on the OneDrive client.
Powershell Commandlets: Set-SPOTenantSyncClientRestriction | Docs
Source article: Block syncing of specific file types - OneDrive | Microsoft Docs
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