Mail search not working on OS Sierra 10.12

Hello, I've just upgraded to Sierra and now mail search doesn't work - no emails appear when I search for anything in mail. Followed some steps about going in to spotlight in system preferences and clicking and un clicking mail - this sadly hasn't worked for me. I tried last week removing the envelope folders and that took my mail out of action for about 4 hours - this also hasn't worked! So frustrating as I have thousands of emails and can't search for any. Any help would be greatly appreciated. Thanks