Unexpected Increase in Exchange Incremental Data Processed By Veeam Backup for Microsoft 365

Issue Summary

First Occurrence — August 7 → August 21, 2023

Some customers using Veeam Backup for Microsoft 365 to back up Microsoft 365 Exchange data may have experienced an unexpected increase in the volume of data being backed up between August 7 and August 21, 2023. Microsoft confirmedMicrosoft has confirmed this issue in the message EX6700041, which will be displayed in the Microsoft 365 Admin Center of some organizations with affected mailboxes. at that time that this was due to a limited incident, which caused older emails to resurface unexpectedly in some Microsoft Exchange Online environments, resulting in increased email data in some Exchange Online mailboxes.

Second Occurrence — March 8 → April 23, 2024

Beginning on March 8^th, 2024, Veeam Support started to receive reports from customers about an unexpected increase in the amount of Exchange data being backed up. Based on the experience with the first occurrence of this issue, Veeam's development team promptly engaged with Microsoft Support to begin investigating the root cause. On April 23rd, Microsoft provided the statement below to address this instance.

Third Occurrence — May 28 → June 12, 2024

Around May 28^th, Veeam Support received reports from customers observing an unexpected increase in the amount of Exchange data being backed up. Veeam's development team engaged with Microsoft Support, and we believe the core issue has been resolved and that no further impact should occur. Microsoft has released a statement regarding this occurrence.

Fourth Occurrence — Late August 2024 → September 2024

Around Aug 16^th, Veeam Support received initial reports from customers observing an unexpected increase in the amount of Exchange data being backed up. Veeam's development team is engaged with Microsoft Support to learn if this issue is the same as the previous occurrences and is working towards a mitigation strategy.

Around September 3^rd, Microsoft published event EX870973, which is expected to be present in the Service Health dashboard for all affected tenants. This direct communication from Microsoft addresses the situation and identifies that the root cause may have been isolated (specific delays with EWS requests in Exchange Online resulted in an increased number of events and items to back up). The statement goes on to explain that a remediation plan is currently being processed to resolve this issue by September 20^th.

On October 10th, Microsoft support followed to explain that, the issue had been resolved as of September 27th. We are told that the necessary fixes were deployed and should result in a return to normal operation between 4-6 weeks depending on roll-out.

Backup Impact

Emails that were changed, causing them to resurface unexpectedly, must be captured by Veeam Backup for Microsoft 365 to ensure backup continuity. Even though these emails may have been previously backed up, their modified state means they must be backed up again. There is no way to reclaim the space utilized by the backup of these resurfaced emails, as it is technically changed data.

This situation is discussed in further detail in Veeam's RND forums.