Support teleporting doors for pathfinding
It's not an original Morrowind feature. But it is possible to implement it using recastnavigation.
OpenMW has non-teleporting doors support for pathfinding. There is off-mesh connection a special entity on navmesh for this. It connect's any two points in the same navmesh. Actor assume it will be teleported from one point to another using given path. But now it is not teleporting anywhere. Another part of OpenMW handles situation when actor is near closed door. It just opens door when right before it reach first off-mesh connection point. Then this point is removed from path as reached and actor just goes to the next.
Teleporting doors require to have navmesh for both interior and exterior cells at the same time. Off-mesh connection will use teleport points to link navmesh points. Somehow actor should activate door being near it right when path point is removed. It should check a condition is next point is a teleport start and is it close enough to use an activator. Otherwise it will try to go directly to the next one (teleport destination) through a wall without any success.
Another problem is path between two different interior cells through an exterior. For this coordinates of objects in interior cells should not overlap. They are overlap right now, because all interior cells has same world coordinates.
To resolve this issue start from here.