Clients upgrading from 'classic' to the Azure-based platform might experience below error when the Xink client is trying to update email signatures:
Remove this setting in your 'classic' console:
Removing the above setting will NOT remove read-only protection.
Removing the setting will prevent read-only to be reapplied when users log in to the domain.
Make sure you remove read-only protection for all domain users in their Outlook signature folder: