Under Options/General/Systems Integration, there is a box 'Allow Windows Search to search messages'. It's sometimes recommended to leave it unchecked, to avoid performance losses. See para. 4 here.

Thanks, but that was already checked. Windows 10 only seems to want to search outlook accounts. Not sure how to resolve the problem.

I've never used Windows Search for email, but I'd check the W10 Searching Windows settings to ensure the TB profile folder is included. Even though you've selected the Enhanced option, check Advanced Search Index Settings.

What part of searching in TB, Classic, Global or Quick Filter, do you find inadequate? There is also a Windows app, MailStore, for archiving and searching email.

I do not find Thunderbird inadequate for searching. I was looking to see if I could improve my workflow by using Windows search. It works very well with documents. I was wondering it it could do the same for email. I crawled through the advanced settings for Windows search and have made the index to include all app data. I will see if that works as well. If not I will stick with TBird.

My personal inclination about windows search in Thunderbird is it is clunky and really not at all useful.

The process creates a WDSEML file in your Thunderbird profile for each email you have (in my case hundreds of thousands) windows search then finds the text of the email and does not know what to do with it other than try and open the wdseml file (which is not the email Thunderbird has) All in all I disabled it, manually deleted the 150,000 odd files that were clogging up my windows backup and about halved the storage requirements for my profile folder (it now fits on a USB drive again)

I also found that with windows indexing in my profile Thunderbird was an on again off again product that spent half it's time simply frozen.