Comments from Dave Kosak on the portals to and from Draenor:
Q: … Or if they are simply a convenience thing. Please answer! Us roleplayers would love to know!
A: In lore those portals probably aren’t running 24/7. But a garrison commander could certainly order them opened. (DaveKosak)
In game, NPCs are acknowledging portals for once, so it seems like they DO exist in lore this time, just gotta get the mages to expend the energy.
This is what started that conversation: