M365 SecureStore - Mailbox Restore Troubleshooting

Failed to open mailbox: <customer's mailbox>

When you are restoring a mailbox, the Global Admin account that is used must have ApplicationImpersonation role.

This role can sometimes be missing, resulting the following errors:
      Failed to access mailbox. Mailbox does not exist.

You need to run the following PowerShell commands at the OS where Veeam B&R with Exchange Explorer is installed/run:

Install-Module -Name ExchangeOnlineManagement -Scope CurrentUser

Connect-ExchangeOnline -UserPrincipalName <your Global Admin account>

New-ManagementRoleAssignment –Role ApplicationImpersonation –User <your Global Admin account>

Restore Operation Timeout

Default timeout period for .NET framework is short and this may cause restore operation timeout error when restoring large mailbox.

You need to extend the timeout period by altering the config file at the OS where Veeam B&R with Exchange Explorer is installed/run.

• Stop and close the Veeam Exchange Explorer (if still open and running).
• Open config file - C:\ProgramData\Veeam\Backup\ExchangeExplorer\Config.xml
• Add the following text between the tags in the file:

<Veeam>
    <Archiver>
        <WCF OperationTimeout="3600" />
    </Archiver>
</Veeam>

• Save the file.
• Re-launch the Veeam Exchange Explorer again to restore mailbox.

Failed to Connect to Service Provider or Error During Mailbox Export

Some versions of Veeam Explorer for Microsoft Exchange would throw the following error when trying to connect in the Service Provider dialog page:

      Handshake failed. Unable to read beyond the end of the stream.

Or throw the following error when trying to restore/export mailbox data:

      Invalid setrialized stream, unknown opcode found: 4

Verify the Veeam Explorer for Microsoft Exchange file version you are using:

• go to - C:\Program Files\Veeam\Backup and Replication\Explorers\Exchange
• locate file Veeam.Exchange.Explorer.exe
• right-click and select Properties > Details

If file version is older than 12.1.0.2031, please apply the patch VeeamExplorerForExchange.msp.

If file version is newer than 12.1.0.2031, please uninstall the Veeam Explorer for Microsoft Exchange and install VeeamExplorerForExchange.msi, followed by patch VeeamExplorerForExchange.msp.

(Links to download files are below)