Shadowforge City needs to be removed from the Blackwing Descent section, that is an instanced starting area for the the dark iron dwarves. You cannot get to the open world from that area without teleporting back out to I believe Stormwind City.
I didn't know mages could port to Swamp of Sorrows wth...Surprised this is actually the first time I've heard of such portal.
Old news, I know. But if Alliance ports to Stormwind, it is a super short direct flight. No need to take a taxi anywhere.