How Outlook for Windows connected to Exchange Online utilizes Microsoft Search

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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

 

Scenario	Details
Primary Mailbox – Cached Mode	Complete
[Explicitly Added] Shared Mailbox	Complete
All Mailbox scoped search	Complete, available in builds >= 16.0.12716
KQL Terms	Partially migrated – From, To, CC, Subject, HasAttachments, IsRead, Importance, Kind, and Size use Microsoft Search All other special KQL terms continue to rely on local searchMAPI restrictions Note: New date picker in Advanced Search will leverage Microsoft Search

 

 

Migration to Microsoft Search In Progress

 

Scenario	Details
Primary Mailbox – Online Mode (i.e. not Cached Mode)	Available in Current Channel (Preview) builds >= 16.0.12022  Note By default, accounts run in Cached Mode. Online Mode is not related to Internet connection status.
Online Archive	Available in Current Channel (Preview) builds >= 6.0.12410
Unlimited Archive (AKA Auto Expanding Online Archive)	Available in Current Channel (Preview) builds >= 16.0.12716
[Explicitly Added] Delegate Access	Not working – Under investigation
Subfolder scoped search	In progress – Available in Current Channel (Preview) builds >= 16.0.12022
Primary Calendar Search	In progress – Not yet available
Shared Calendar	Not started – Local search uses Windows Search. Online search uses MAPI restrictions
Delegate Access Calendar	Not started – Local search uses Windows Search. Online search uses MAPI restrictions

 

 

Not planned for migration to Microsoft Search

 

Scenario	Details
Shared Folder	No plans to migrate – Local search uses WDS. Online search uses MAPI restrictions.
Public Folder	No plans to migrate – Local search uses WDS. Online search uses MAPI restrictions.
[Automapped] Shared Mailbox	No plans to migrate – Local search uses WDS. Online search uses MAPI restrictions.
[Automapped] Delegate Access	No plans to migrate – Local search uses WDS. Online search uses MAPI restrictions.
All Outlook Items Search	No plans to migrate – Local search uses WDS. Online search uses MAPI restrictions.
Group Search	No plans to migrate – Local WDS search only.
Work Offline	No plans to migrate – By nature of the scenario, only local search is supported.

 

Brought to you by Dr. Ware, Microsoft Office 365 Silver Partner, Charleston SC.