Since the start of this week, several of my Veeam Backup for Microsoft 365 installations are reporting an error. I decided to address these errors.

The situation

I'm using Veeam Backup for Microsoft 365 as a means to create backups of data in Microsoft 365 services (Exchange Online, SharePoint Online, OneDrive for Business) to a backup repository on Azure storage. If anything goes wrong, I can restore data granularly.

In the organizations, no Public Folders are in use in Exchange Online.

After upgrading to the latest version earlier this year, these setups have worked without errors. No changes have been made recently in Entra or Microsoft 365.

The issue

Suddenly, starting this week, I'm getting the following error when processing mailboxes in Exchange Online:

Processing mailbox failed with error: Failed to get folder properties. Not allowed to access Non IPM folder.

The cause

According to the Veeam help center, the error is returned from Microsoft Exchange upon an attempt to access a Non IPM folder, resulting in ErrorAccessDenied. Yet, these organizations don't use the Public Folders feature in Exchange Online…

The issue is caused by the hidden TeamsMessagesData folder that has been used in the past for journaling Teams messages. Until earlier this week, Microsoft has not blocked access to this folder after the access via EWS APIs was deprecated and new paid APIs were introduced.

The solution

To solve these errors, I followed the steps that Kay van Aarssen shared on the Veeam Forums:

• Sign in to the Windows Server installation that runs Veeam Backup for Microsoft 365.
• Open the Services MMC Snap-in (services.msc)
• Stop the following services:
  • Veeam Backup for Microsoft 365 Service
  • Veeam Backup Proxy for Microsoft 365 Service
• Open File Explorer.
• Go to: C:\ProgramData\Veeam\Backup365.
• Make a copy of the Config.xml file.
• Open the Config.xml file in Notepad.
• Add the following line right under the </Archiver> tag:

<Proxy SkipTeamsMessagesDataFolders="True" />

• Save the file and exit Notepad.
• Close File Explorer and switch back to the Services MMC Snap-in.
• Start the following services:
  • Veeam Backup for Microsoft 365 Service
  • Veeam Backup Proxy for Microsoft 365 Service
• Close the Services MMC Snap-in
• If you have multiple Veeam Backup Proxies:
  • Open Veeam Backup for Microsoft 365 Console.
  • Navigate to Backup Infrastructure, then Backup Proxies
  • Right-click on the other proxies and select Upgrade from the context menu.
  • In the step for the credentials make sure to use: HOSTNAME\USERNAME and the password.

After these steps, I retried the backup of the mailboxes in Exchange Online. The backups were succesful then.