Kill Arazzius the Cruel, then return to Nazgrel in Thrallmar.
Magister Bloodhawk finally deciphered the Legion missive you found earlier. It turned out to be attack plans sent by one of Highlord Kazzak's lieutenants - Arazzius the Cruel. Apparently, Arazzius commands the Legion ground forces in Hellfire. The time has come to terminate his command, [player]. Terminate with extreme prejudice.
Head west to the Pools of Aggonar and put an end to this so-called 'Legion lord'. Today, the Horde reclaims Hellfire Peninsula. Let the Legion be damned.