My trade is swords and secrets, which is a difficult trade to deal in when men more powerful than you, men who trained you and rebuilt you from the ruins of war and the bottom of a barrel of wine, come to hunt you.
It's hard to deal in trade when people better than you want to kill you.
Second, further work would likely allow us to develop, for a higher percentage of outbound DC mail, (1) estimates of the domestic postage costs that would be incurred if the Postal Service paid domestic postage instead of terminal dues and, (2) the outbound mail revenues associated with such mail flows.