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Go to Control Panel, Indexing Options, make sure Outlook and Users both show in Locations, and then click on Advanced and Rebuild the Windows Index. This will take a couple of hours.<br />
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Now open Outlook, Options, Search and make sure the settings are correct. Current Folder may not find much, but Current Mailbox or All Mailboxes should find what you want. <br />
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This is how I set Outlook.
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Go to Control Panel, Indexing Options, make sure Outlook and Users both show in Locations, and then click on Advanced and Rebuild the Windows Index. This will take a couple of hours.

Now open Outlook, Options, Search and make sure the settings are correct. Current Folder may not find much, but Current Mailbox or All Mailboxes should find what you want.

This is how I set Outlook.

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Create a restore point in Windows,<br />
If outlook is in cached mode, &nbsp;take it out of cached mode, shut down outlook, &nbsp;then delete the OST. &nbsp;Run outlook then put it back in to cached mode, and retest.
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Create a restore point in Windows,
If outlook is in cached mode,  take it out of cached mode, shut down outlook,  then delete the OST.  Run outlook then put it back in to cached mode, and retest.

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I am using Outlook 365 and have been for the past few years - this is on a Windows 10 Professional system. &nbsp;Everything has worked fine up until about a week ago and I can no longer use the search function - every time I put something in, it comes back no results. &nbsp;I have re indexed the information as well as going into the Options, Search - unchecking Outlook and re-checking it, which seemed to work for about that long but went back to no results. &nbsp;If I totally uncheck the box, it will give me a message about Something went wrong and your search couldnt be competed - however it searches thru every folder bringing up stuff
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I am using Outlook 365 and have been for the past few years - this is on a Windows 10 Professional system.  Everything has worked fine up until about a week ago and I can no longer use the search function - every time I put something in, it comes back no results.  I have re indexed the information as well as going into the Options, Search - unchecking Outlook and re-checking it, which seemed to work for about that long but went back to no results.  If I totally uncheck the box, it will give me a message about Something went wrong and your search couldnt be competed - however it searches thru every folder bringing up stuff

Outlook 365

Windows 10 is a personal computer operating system featuring the "universal application architecture" (UAP); apps can be designed to run across multiple devices with nearly identical code, including PCs, tablets, smartphones, embedded systems, Xbox One, Surface Hub and HoloLens. Windows 10 also includes a virtual desktop system, a window and desktop management feature called Task View, the Microsoft Edge web browser, support for fingerprint and face recognition login, voice-based search (Cortana), new security features for enterprise environments, and DirectX 12 and WDDM 2.0 to improve the operating system's graphics capabilities for games.

Windows 10

Microsoft Outlook is a personal information manager from Microsoft, available as a part of the Microsoft Office suite. Although often used mainly as an email application, it also includes a calendar, task manager, contact manager, note-taker, journal, and web browser.

Outlook

Office 365 is a group of software plus services subscriptions that provides productivity software and related services to its subscribers. Office 365 allows the use of Microsoft Office apps on Windows and OS X, provides storage space on Microsoft's cloud storage service OneDrive, and grants 60 Skype minutes per month. Office 365 includes e-mail and social networking services through hosted versions of Exchange Server, Skype for Business Server, SharePoint and Office Online, integration with Yammer, as well as access to the Office software. All of Office 365's components can be managed and configured through an online portal; users can be added manually, imported from a CSV file, or Office 365 can be set up for single sign-on with a local Active Directory using Active Directory Federation Services.