Failed to open mailbox abc@abc.onmicrosoft.com" "failed to access mailbox" " Mailbox does not exist"

 

Applies to : Veeam Backup for O365, Exchange Server 2013, 2016, 2019

Problem:  Cross Tennent Veeam backup restore error " Failed to open mailbox abc@abc.onmicrosoft.com" "failed to access mailbox" " Mailbox does not exist"

Scenario: I have Two Office 365 Tennent "A" and "B", I want to migrate all mailbox data from Tennent "A" to Tennent "B" ( Cross Tennent Migration ).

I Used the Veeam O365 backup tool to backup of all mailbox,Sharepoint, One Drive data from Tennent "A" and Create Restore Task to Tennent "B".

Diagnose : 

1) Download Backup Logs from Veeam Console. https://helpcenter.veeam.com/docs/vbo365/guide/vbo_exporting_logs.html?ver=60 

2) Found below error in log file.

Resolution : 

1. Login to the Office 365 Exchange Admin Portal.

2. Go to Permissions, then under Admin Roles click the '+' symbol to add a new role and enter the Name and Description 'CloudMigratorImpersonation'.

3. Click the '+' symbol under 'Roles:', select ApplicationImpersonation, click 'add →' then 'OK'

4. Click the '+' symbol under 'Members:' and select your Admin User, click 'add →' then 'OK'

5. Click 'Save' in the 'Role Group' window and you will then see the Impersonation role listed in Admin Roles. 

You can now use application impersonation with your admin user in CloudMigrator.

Reference : 

https://answers.microsoft.com/en-us/msoffice/forum/all/exchange-impersonation-error-unable-to-open-user/834c4ea9-6cb5-4df4-9011-433ba501f6d2

https://www.techieshelp.com/exchange-2013-configuring-impersonation-applications/