"Mailbox is not fully configured" Error During Exchange Backup

A backup job may fail when processing Archive Mailbox objects with the following error:

Processing archive mailbox: username@organization.com failed with error: Mailbox is not fully configured.

• This issue was resolved in Veeam Backup for Microsoft 365 8.2 P20251031 (build 8.2.0.2202) available from KB4751.
  Critical Note: After updating Veeam Backup for Microsoft 365, you must upgrade all proxies.
• As of 2025-11-01 this issue is resolved for all customers using Veeam Data Cloud for Microsoft 365. For more information, please review https://vdcstatus.veeam.com/.

Updates

• 2025-11-06
  A fix is now available for Veeam Backup for Microsoft 365 8.2 via KB4751. This issue is now fixed in Veeam Backup for Microsoft 365 build 8.2.0.2202.
  
• 2025-11-01
  A patch has been deployed for Veeam Data Cloud for Microsoft 365, and this issue is now fixed for all customers using Veeam Data Cloud for Microsoft 365.
• 2025-10-24
  • An updated release of Veeam Backup for Microsoft 365 8.1.2, containing a fix for this issue, is now available via KB4711.
  • Veeam RND is working on a fix for Veeam Backup for Microsoft 365 8.2.
• 2025-10-23
  The root cause has been identified, and we are finalizing a solution. We appreciate your patience as we work to resolve this issue as quickly as possible.