Mail search function not working

You first need to update to Sierra 10.12.6. The update might fix your Spotlight issues. If not you will need to reindex Spotlight as Eric described.

I highly suggest you backup first before updating.

Download macOS Sierra 10.12.6 Combo Update

https://support.apple.com/kb/DL1931

Post Date: Jul 19, 2017

File Size: 1.98 GB

Try re-indexing Spotlight.

Spotlight – Re-index

According ti the article macOS Sierra: If searching your Mac doesn’t return expected results

Check the location you’re searching

If you began your search in Spotlight, the search results can include email, Calendar events, Spotlight Suggestions, information from other apps, and more. If you began your search in a Finder window, the search results include only files and folders on your internal disk.

Read the steps in the article , perhaps its best to take back up of all mails and configure once again .

Click on Go on top menu bar , hold option key click on > library > select mail folder > right click on mail there itself > click on copy mail > right click on extreme right hand side in column B , that is below persistence info.plist > click on paste item .

Entire mails are copied to V4 folder .

Go to the corrupted IMAP account > open its preferences > select Accounts > select the account that has to be deleted & click on minus sign .

Configure new IMAP account , go to top menu bar , file > import mail boxes > import data from > select apple mail > click on continue > select the back drop folder then choose new .

When new IMAP account is opened , a new folder with all mails will appear in the mail side bar .You can rename the folder .