Challenge
Due to a recent change deprecating an earlier API (EWS), backups of Microsoft Teams may complete with a "Success" status, while no new channel posts were backed up.
Solution
As it was announced before, Microsoft is deprecating the ability for EWS APIs to access the TeamsMessagesData folder.
In order to resume backup functionality, you must accept Microsoft's Terms of Service for the newer Graph Export API for Teams. Please review KB4322 and take the prescribed actions to ensure all Teams data including channel posts is protected.
More Information
Microsoft Devblog: Restricted access to Microsoft Teams data via EWS starts January 31, 2023
Veeam KB4322: How to request access to Microsoft Graph Teams Export APIs
Veeam KB4340: How To Configure Veeam Backup for Microsoft 365 to Use Microsoft Graph Export API for Teams
