Blacknails, a member of the Defias Brotherhood mentioned in , is probably the person in charge of Jangolode Mine or Gold Coast Quarry (or both), since the Defias Messenger, the carrier of the letter, is walking between the Deadmines and these two places (probably delivering it from Edwin VanCleef to Blacknails).
Not much is currently known about Blacknails, including what race and of which sex he/she really is.
Who is Blacknails?
Blacknails is only mentioned in and nowhere else in the game or the Warcraft Universe. He/she appears to be well-known by VanCleef, trusted with "coming through" for him while other suppliers have not.
Some speculate that Blacknails may be Katrana Prestor, a black dragon with known connections to the Defias Brotherhood, however, it is most likely a nickname given to one of the Defias members located at either the Gold Coast Quarry or Jangolode Mine.
Details may become clearer in Cataclysm, when Deadmines will be an instance with a heroic setting.