Veeam Support Knowledge Base
Exchange Backups failing with "Failed to access mailbox" starting September 13th, 2023

Exchange Backups failing with "Failed to access mailbox" starting September 13th, 2023

KB ID:	4494
Product:	Veeam Backup for Microsoft 365 \| 6.0 \| 7.0
Published:	2023-09-15
Last Modified:	2023-09-19

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Challenge

Starting on September 13, 2023, some customers using Veeam Backup for Microsoft 365 to back up Microsoft 365 exchange data may have backup jobs fail to process mailboxes with the error:

Failed to access mailbox.. An internal server error occurred. The operation failed.

Cause

Microsoft has confirmed that this issue is related to the incident they've documented in their Health Dashboard as EX675238, which caused some Microsoft Exchange Online environments to have issues with RESTAPI calls used to access the mailbox externally.

Solution

The Microsoft investigation has been completed. According to the Microsoft 365 Service Health Dashboard's EX675238, the team has finished the configuration changes to expedite resolution and confirmed via service health telemetry information that all impacted scenarios have been remediated successfully.

As this issue is no longer active, this Veeam KB article will be auto-archived in 30 days (2023-10-19).

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