> For the complete documentation index, see [llms.txt](https://helpcenter.xopero.com/xopero-one-en/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://helpcenter.xopero.com/xopero-one-en/common-issues/microsoft-365/ost-files-are-not-included-in-backup.md).

# OST files are not included in backup

## Issue

> OST files are excluded from backup.

***

## Cause

{% hint style="warning" %}
The exclusion of **OST** files is not accidental—learn more on the [**Microsoft Tech Community** website](https://techcommunity.microsoft.com/t5/storage-at-microsoft/why-completepc-backup-does-not-include-ost-files-in-the-backup/ba-p/423354).
{% endhint %}

**Xopero ONE** uses the **Microsoft Volume Shadow Copy Service** (**VSS**) for backup tasks. Certain files, such as deleted, temporary, paging, and **OST** files, are excluded from snapshots. This exclusion is managed by the `FilesNotToSnapshot` registry key in **Windows** registry. Consequently, these files are bypassed during the snapshot process and **are not included in the backup**.

***

## Resolution

The excluded **OST** files can be found under `FilesNotToSnapshot` in **Registry Editor** (**regedit**)—you can include these files in **VSS** by removing specific values from the registry key:

1. Open **Registry Editor** (search box on the **Windows** taskbar > type **regedit** > select **Registry Editor**).
2. Navigate to `HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\BackupRestore\FilesNotToSnapshot`.
3. Remove `OutlookOST` value.

<figure><img src="/files/debsLAlLbjJjbAlLq5lI" alt="FilesNotToSnapshot registy key in the regedit"><figcaption></figcaption></figure>


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