Backup Size Discrepancy in Microsoft 365 and Google Workspace

In some cases, the backup size reported in the backup solution may differ from the storage usage shown in Microsoft 365 or Google Workspace admin portals. This discrepancy is expected behavior and is primarily related to how data is stored, processed, and backed up.

This article explains why such differences can occur, with a focus on Exchange Online email backups and SharePoint backups.

Exchange Online – Email Backup

When backing up Exchange Online mailboxes, the reported backup size may be significantly smaller than the mailbox size displayed in the Microsoft 365 admin center. This can happen for several reasons:

• System and synchronization data is not backed up
  The backup includes only relevant user data. Microsoft 365 system data, such as Outlook synchronization folders and other service-related metadata, is excluded from backups.

• High compression ratio
  Email data consists mostly of text, which is highly compressible. Compression can reduce the size of backed-up email data by up to 94%, resulting in a much smaller backup footprint compared to the original mailbox size.

• Mailbox statistics vs actual data
  The size reported by Exchange Online includes internal service data and metadata that are not part of the actual email content and therefore are not included in the backup.

As a result, it is normal for Exchange Online email backups to appear much smaller than the mailbox sizes shown in Microsoft 365.

SharePoint

A discrepancy between SharePoint storage usage and backup size may also occur due to the following factors:

• Selective data backup
  Only relevant SharePoint content is backed up. Microsoft 365 system data and service-related metadata are not included.

• Versioning behavior
  File versions created before the first backup are not backed up. Only new file versions created after the initial backup are included. This can significantly reduce the overall backup size, especially in environments with extensive version history.

• Compression
  As with other data types, compression is applied to SharePoint content, further reducing the storage size of the backup.

Because SharePoint storage usage often includes extensive version history and system data, the backup size may be noticeably smaller.

General Notes on Backup Size

In both Microsoft 365 and Google Workspace environments, backup size depends on several factors:

• Only relevant user data is backed up

• System, service, and synchronization data is excluded

• Compression significantly reduces storage requirements

• Historical file versions created before the first backup are not included

These factors combined explain why backup sizes should not be expected to match the storage usage reported by Microsoft 365 or Google admin portals.