Hello!
I am creating a room that has multiple door exits. (As shown in screenshot) And I need to export to .obj to use within unity, now this room is made with a box that has been intruded and then the door frames have been made with separate boxes, where I have selected one door box, and then the room box that I then used Mesh/ boolean/ union to remove the space within; this I did 3 times. Then I exported as an .obj file and re-imported to maya to check the file and it came out like that (Look at screenshot).

The bottom box is the original, un-exported file, and the top one is the exported file that was imported for checking.
(https://gyazo.com/4f75a7394494d2488a0f0f8d088b61b4)