> For the complete documentation index, see [llms.txt](https://docs.material.security/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.material.security/learn-more/administration/mailbox-mirroring.md).
# Mailbox Mirroring
## Overview
By default, Material retains metadata for deleted messages to ensure your team has historical data available for future audits, post-incident investigations, and compliance reporting.
However, if your organization has strict data minimization policies, **Mailbox Mirroring** allows you to change this behavior. When enabled, Material permanently deletes its retained data when the message is permanently deleted from the source mailbox. This ensures Material never holds the sole remaining copy of a message, which helps you meet specific legal, privacy, or corporate retention mandates.
Mailbox Mirroring in Settings
{% hint style="warning" %}
**Availability Note:** Material must enable this feature for you. Mailbox Mirroring is **only available for dedicated instances**; it is not supported on shared instances.
Contact Material Support to check your eligibility or request enablement.
{% endhint %}
### Trigger Conditions
Material treats a message as "permanently deleted" and triggers Mailbox Mirroring when any of the following conditions are met:
* **API Inaccessibility:** The message is permanently deleted from the mailbox and is no longer accessible via the [Gmail API](https://developers.google.com/gmail/api/reference/rest/v1/users.messages/get) or [Microsoft Graph API](https://docs.microsoft.com/en-us/graph/api/message-get?view=graph-rest-1.0\&tabs=http).
* **Account Deletion:** The user account containing the message is permanently deleted.
* **Instance Unenrollment:** The instance containing the message is unenrolled from Material.
#### Key Notes & Exceptions
* **Secured Messages:** When Material secures a message, the secured version replaces the original. Material does not treat the original message as deleted until the secured version is also deleted.
* **Suspended/Archived Accounts:** Accounts that are merely suspended or archived are not treated as permanently deleted.
* **Outlook Folder Specifics:** Messages in folders like `Purges`, `Versions`, and `SubstrateHolds` do count as deleted because end users cannot access them.
* Messages in `ArchiveRecoverableItemsDeletions` do not count as deleted because end users can still recover them.
### Interaction with Material Protections
Some Material protections, like [Email Data Security](/learn-more/risk-areas/email-data-security.md), replace a standard mailbox message with a secured version. For Mailbox Mirroring, deleting this secured version is treated exactly the same as deleting the original message.
#### Critical Risk: Critical Risk: Actions That Can Cause Permanent Data Loss
Certain user or admin actions keep the message content but change the underlying message or account ID. Mailbox Mirroring cannot distinguish these changes from a true deletion. If an ID changes, Mailbox Mirroring may trigger and render the message permanently unretrievable. Review these common scenarios before enabling the feature:
| **Action / Scenario** | **Technical Impact** | **Result** |
| -------------------------- | --------------------------------------------------------------------------------------------------------- | -------------------------------------- |
| Archiving in Outlook | Moving a secured Outlook message to the archive mailbox changes its immutable ID. | Message becomes unretrievable. |
| M365 Instance Migration | Migrating an account to a new instance without first uninstalling Data Protection changes the account ID. | Secured messages become unretrievable. |
| Google Workspace Migration | Deleting an account and migrating its messages to a new account changes the message ID and user ID. | Messages become unretrievable. |
| API Rewriting | Rewriting a secured stub with another application which changes the message ID. | Message becomes unretrievable. |
| Copying & Deleting | Copying a secured Outlook message to another folder and deleting the original changes the message ID. | Message becomes unretrievable. |
#### Next Steps
Before enabling Mailbox Mirroring alongside mailbox-level protections, carefully plan for upcoming migrations, user off-boarding, and mailbox architecture changes.
* For information on how settings apply across your deployment, see [Settings Hierarchy](/learn-more/administration/settings-hierarchy.md).
* For specific off-boarding guidance, see [Off-board Users](/learn-more/administration/off-board-users.md).
***
### FAQ
#### Why would I leave Mailbox Mirroring off?
Material recommends leaving Mailbox Mirroring off unless your organization has specific legal or regulatory requirements for data minimization. Retaining metadata for deleted messages helps with investigations, incident response, and reporting. It also preserves data that supports [Message Search](/getting-started/fundamentals/explore/message-search.md), even after a message is permanently deleted from the source mailbox.
#### How long does deletion take?
Mailbox Mirroring starts processing only after the email provider's built-in recovery window expires and the deletion becomes permanent. End to end, it can take up to **90 days** for Material to fully delete the message data.
#### What data does Mailbox Mirroring delete?
When triggered, Material deletes:
* The stored copy of the original message (if applicable).
* The metadata associated with that message, including data used by [Message Search](/getting-started/fundamentals/explore/message-search.md) and analytics.
**What is not deleted?**
* Message metadata tied to **Email Threat issues** is retained to preserve historical security context.
* **Debug logs** that may contain metadata are excluded and follow a standard 180-day retention policy.
---
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