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.