When you search in Outlook, the results may only show items from your primary mailbox. This happens because the Microsoft Search tenant setting for cross-mailbox search is not enabled. The feature allows Outlook to search across shared mailboxes, group mailboxes, and public folders in addition to your own mailbox. This article explains how to enable the Microsoft Search tenant setting and configure it for your organization.
Without this setting, users cannot find emails stored in shared mailboxes they have permissions to access. The setting is managed in the Microsoft 365 admin center and requires a global admin or Exchange admin account. After enabling it, Outlook for Windows, Outlook on the web, and Outlook for Mac will all return results from multiple mailboxes.
This guide covers the exact steps to enable the setting, what each option does, and what to do if cross-mailbox search still does not work after configuration.
Key Takeaways: Enabling Cross-Mailbox Search in Outlook
- Microsoft 365 admin center > Search & intelligence > Search & intelligence settings: The main location to enable cross-mailbox search for your tenant.
- Allow search across multiple mailboxes toggle: Turns on the ability for Outlook to return results from shared mailboxes, group mailboxes, and public folders.
- Exchange admin center > Shared mailboxes > Edit delegation: Use this to verify that users have Full Access or Send As permissions on the shared mailbox.
Overview of the Microsoft Search Tenant Setting for Cross-Mailbox Search
The Microsoft Search tenant setting controls whether Outlook can search across multiple mailboxes that a user has permission to access. By default, this setting is disabled for most organizations. When disabled, Outlook only searches the user’s primary mailbox and ignores shared mailboxes, group mailboxes, and public folders.
The feature relies on the Microsoft Search service, which indexes all mailbox content in the cloud. When cross-mailbox search is enabled, the search query is sent to the Microsoft Search service, which returns results from all mailboxes the user has permissions to view. This applies to Outlook for Windows (version 2002 or later), Outlook on the web, and Outlook for Mac.
There are no prerequisites for the end user beyond having the correct permissions on the target mailbox. The admin who enables the setting must have a global admin or Exchange admin role. The change takes effect within 15 minutes for most tenants.
Steps to Enable the Microsoft Search Tenant Setting
Follow these steps to enable cross-mailbox search for all users in your organization.
- Sign in to the Microsoft 365 admin center
Go to admin.microsoft.com and sign in with an account that has global admin or Exchange admin privileges. In the left navigation pane, click Show all to expand the full menu. - Open Search & intelligence
Under the Admin centers section, click Search & intelligence. This opens the Microsoft Search management dashboard. - Navigate to Search & intelligence settings
In the left pane of the Search & intelligence page, click Search & intelligence settings. This is the top-level settings page for all search features. - Click Content and people
On the Search & intelligence settings page, scroll down to the Content and people section and click it. This section contains settings for mailbox search. - Enable cross-mailbox search
Under Mailbox search, locate the toggle labeled Allow search across multiple mailboxes. Click the toggle to turn it on. The toggle will change from gray to blue. - Save the setting
Click Save at the bottom of the page. A confirmation message appears indicating the setting has been applied. - Verify the setting is active
Open the same page again after five minutes. The toggle should remain in the On position. If it has reverted to Off, repeat the steps and ensure you clicked Save.
After enabling the setting, users must close and reopen Outlook to apply the change. Cross-mailbox search will work for Outlook for Windows, Outlook on the web, and Outlook for Mac. No additional configuration is needed on the client side.
If Outlook Still Does Not Search Across Mailboxes After Enabling the Setting
User does not have permission to the shared mailbox
The Microsoft Search setting only enables the feature. Users still need explicit permissions on each shared mailbox. To grant permissions, go to the Exchange admin center at admin.exchange.microsoft.com. Navigate to Recipients > Mailboxes, select the shared mailbox, and click Mailbox delegation. Under Read and manage, add the user and click Save. The user must have at least Full Access permission to see results from that mailbox.
Outlook client version is too old
Cross-mailbox search requires Outlook for Windows version 2002 (build 12527.20000) or later. To check the version, open Outlook, click File > Office Account > About Outlook. If the version is older, update Outlook through the Microsoft 365 Apps update channel: File > Office Account > Update Options > Update Now.
Search is still returning only the primary mailbox
If the setting is enabled and permissions are correct, the search index may need to rebuild. In Outlook for Windows, go to File > Options > Search > Indexing Options > Advanced > Rebuild. This forces a full reindex of all mailboxes. The rebuild process can take several hours for large mailboxes.
The setting was applied but reverted
Some organizations use group policies or configuration profiles that override the Microsoft 365 admin center setting. Check if any Microsoft Search policies are deployed via Intune or Group Policy. If a policy is set to Disabled, it will override the tenant setting. Remove or set the policy to Not Configured.
Cross-Mailbox Search vs Default Mailbox Search: Key Differences
| Item | Cross-Mailbox Search (Enabled) | Default Mailbox Search (Disabled) |
|---|---|---|
| Search scope | Primary mailbox + shared mailboxes + group mailboxes + public folders | Primary mailbox only |
| Permission requirement | User must have Full Access or Send As permission on each target mailbox | No additional permissions needed |
| Performance impact | Slightly slower results because the search query spans multiple indexes | Fast results from a single index |
| Supported clients | Outlook for Windows (2002+), Outlook on the web, Outlook for Mac | All Outlook clients |
| Admin configuration | Requires Microsoft 365 admin center change | No configuration needed |
Enabling the Microsoft Search tenant setting for cross-mailbox search gives users access to all emails across the organization without leaving their primary mailbox. Verify permissions on shared mailboxes after enabling the setting and update Outlook clients to version 2002 or later for full compatibility. For advanced scenarios, consider using the Search-Mailbox PowerShell cmdlet to audit which mailboxes a user can search.