I decided to carry passengers and mail to this factory to see what happened. The step time and i realized that the mail level never increase.
Is this a mistake? or is there any way to increase it? ???
(http://sphotos-b.ak.fbcdn.net/hphotos-ak-prn1/921535_567770783263233_2048559147_o.jpg?dl=1)
Passenger and mail levels for buildings in general are static. I would assume that this applies to factories as well. (Although the definition for a factory actually contains two passenger levels, but only one mail level.)
This factory does not need mail, thus the 0.
You can try sending them email ;)
mmm .. I see, the factory not need email for increase their production , that's why we never increases
thanks VS ;)