Skyrim Ebony Mail Location | Info

You can start the quest any time after reaching level 30, either by reading a copy of Boethiah's Proving or traveling directly to the Sacellum of Boethiah and talking to the Priestess of Boethiah or killing every one of the cultists. If you wait, you may be attacked randomly in the world by Boethiah cultists, who will have a copy of Boethiah's Proving on their corpse.