After a Sierra update, Apple Mail is not searching anymore, and Spotlight provides incomplete results - it does not provide a top lists e.g. searching for "Excel" does not show Excel or it does not provide results in Mail. What should I do now?
I would start with the procedure described in Rebuild the Spotlight index on your Mac:
- Choose Apple menu > System Preferences, then click Spotlight.
- Click the Privacy tab.
- Drag the folder or disk that you want to index again to the list of locations that Spotlight is prevented from searching. Click OK to confirm.
- Select the folder or disk you just added, then click the Remove (–) button to remove it from the list.
- Quit System Preferences. Spotlight will reindex the contents of the folder or disk.
Another approach is to delete Apple Mail's "Envelope Indexes" as suggested in this forum post:
Please delete your Envelope Indexes. For this, first you need to quit Mail, then delete any Envelope Indexes in your user Library/Mail/V2/MailData. Deleting the Envelope Indexes will force Mail to rebuild its database, and then hopefully it will search properly again. (Mail will ask you to "import" your messages," but it's just rebuilding its database.)
That was posted in 2014, and as suggested in this answer you may need to change from "V2" to "V3" or "V4" as appropriate given your system version:
folder name could be different depending on your backuped system, "V2" is for Mavericks, "V3" is for El Cap, "V4" is for Sierra