Lord's Mail in Underground Caves near Ebonheart - Morrowind
Location: Ebonheart, Underground Caves
Video: Location of Lord's Mail Heavy Armor
The best Heavy Armor chestpiece in the game is Lord's Mail which can be acquired from Furius Achilius in the Underground Caves near Ebonheart. Furius is part of an Imperial quest where you need to obtain his armor to complete the quest - however you can visit this location at any point in the game and kill him for his items without the quest.
You'll find the entrance to the Underground Caves just north of Ebonheart; check my map location below for the exact location. In addition to Lord's Mail there are a couple other goodies for you to find in this cave like a Glass Jinkblade and Frostsword, check out this video for their locations.