Microsoft Search
In Microsoft 365, Microsoft Search returns search results based on the context of the application that you are searching from. When searching in Outlook, Microsoft Search is used to search email messages that are in your mailbox. There are plans for later builds to also query the Calendar, files, and other items within Outlook.
For general information on Microsoft Search, see Overview of Microsoft Search.
The evolution of Search in Outlook
It’s hard to imagine an Outlook without search. In its earliest versions, Outlook supported basic filters based on MAPI restrictions. Starting with Outlook 2007, Outlook has utilized Windows Desktop Search (WDS) to index Outlook Data (.pst) and Offline Outlook Data (.ost) files. These data files are normally stored on the local disk, as are the WDS search indexes. Although WDS provides excellent performance using the indexes on the local disk, mailbox sizes have increased while less mailbox data is synchronized to the local disk. This shift has resulted in a clear need for server- and service-powered search solutions.
This is where Microsoft Search comes into the picture. It fully indexes and searches content, while providing rich and intelligent search features that have become an industry norm. Throughout this journey, Outlook has evolved from local and MAPI-restriction searches, to server-based Exchange content indexing, to EWS/FAST search, and now to the most recent service-based iteration, Microsoft Search.
FAST Search continues to be used in Exchange Server 2016 and 2019 versions. For more information about FAST Search, see How Outlook 2016 utilizes Exchange Server 2016 FAST Search
Scenarios where Outlook uses Microsoft Search
This section is organized to help you determine which search solution is being used, based on a specific scenario. The Outlook product group is updating current versions of Outlook desktop, web, and mobile clients to migrate more and more scenarios to use Microsoft Search.
Note If Outlook cannot connect to Microsoft Search, an error message is displayed with a link to perform a local search.
The following tables list Outlook for Windows search scenarios, along with their current status and future plans to onboard them onto Microsoft Search.
Supported on Microsoft Search
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Scenario
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Details
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Primary Mailbox - Cached Mode
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Complete
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Primary Mailbox - Online Mode (i.e., not Cached Mode)
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Available in Monthly Channel builds >= 16.0.12716
Note By default, new Exchange email accounts are configured in Cached Exchange Mode. Online Mode is not related to Internet connection status.
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[Explicitly Added] Shared Mailbox
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Complete
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All Mailboxes scoped search
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Complete, available in builds >= 16.0.12716
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Subfolder scoped search
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Available in Monthly Channel builds >= 16.0.12920
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Primary Calendar search
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Complete
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Online Archive
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Available in Monthly Channel and Monthly Enterprise Channel builds >= 16.0.13519
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KQL Terms
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Partially migrated - From, To, CC, Subject, HasAttachments, IsRead, Importance, Kind, and Size use Microsoft Search
Received as of build 16.0.14314
All other special KQL terms continue to rely on local search\MAPI restrictions
Note: New date picker in Advanced Search will leverage Microsoft Search
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Migration to Microsoft Search In Progress
The Current Channel (Preview) referenced in the following table was formerly called Monthly Channel (Targeted) or Insider Slow. For details on the Current Channel Preview release dates, see https://docs.microsoft.com/en-us/officeupdates/update-history-current-channel-preview.
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Scenario
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Details
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Microsoft 365 auto-expanding archive
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Available in Monthly Enterprise Channel builds >= 16.0.13519
Note Not supported with on-premises primary mailbox. In a hybrid deployment, the mailbox must be an online mailbox configured with a cloud-based archive mailbox.
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[Automapped] Shared Mailbox
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In progress - Not yet available
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[Automapped] Delegate Access
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In progress - Not yet available
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[Explicitly Added] Delegate Access
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In progress - Not yet available
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Shared Folder
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In progress - Not yet available
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Shared Calendar
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Not started - Local search uses Windows Search. Online search uses MAPI restrictions
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Delegate Access Calendar
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Not started - Local search uses Windows Search. Online search uses MAPI restrictions
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Not planned for migration to Microsoft Search
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Scenario
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Details
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Public Folder
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No plans to migrate - Local search uses WDS. Online search uses MAPI restrictions.
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All Outlook Items Search
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No plans to migrate - Local search uses WDS. Online search uses MAPI restrictions.
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Group Search
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No plans to migrate - Local WDS search only.
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Work Offline
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No plans to migrate - By nature of the scenario, only local search is supported.
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