The Ebony Mail is Daedric Artifact found in The Elder Scrolls V: Skyrim
The Ebony Mail has armor equivalent to ebony armor but has a different (much better) look and comes with two unique enchants.
"You are able to move more quietly, and opponents that get too close take 5 points poison damage per second"
To obtain the Ebony Mail you must first be level 32. Once you've reached level 32 Cultists of Boethiah will begin to attack you in the wild. Once they do you can loot them for a book. Reading the book will begin the quest "Boethiah's Calling". Follow the marker on the map to the shrine of Boethiah. Once there you can either talk to all the nice cultists or slay them all. Boethiah will then contact you and ask you to bring a sacrifice. Anyone who will follow you will do but note you will lose all items in their inventory.
After the sacrifice you will be asked to go take out a champion of Boethiah. The Champion will be wearing the Ebony Mail. So once he's dead it's all yours. Returning to Boethiah's shrine will wrap up the quest and confirm your ownership of the ebony mail. Congrats!
The Ebony Mail is a pretty amazing piece of armor. It's the only chest piece that has the ability muffle and it's poison aura will hurt anyone within arms reach while in combat. Most people want it for the amazing visual effect though. When in combat or sneaking you will cloaked in black smoke.
Hope this helps you and don't forget the Ebony Mail is required for the Oblivion Walker Achievement.