Surface again, as a dormant email thread Crossword Clue

 The crossword clue for "surface again, as a dormant email thread" is reemerge.

This is a verb that means to come into view or existence again after a period of being hidden or inactive.

Here are some other possible answers for the crossword clue:

resurface

reappear

reawaken

revive

resurrect

spring up

I hope this helps!