THE ENCYCLOPEDIA GALACTICA
Armstrong Cuthbert is the mega cargo corporation that has the monopoly on delivery of goods around the Galaxy. The company was formed pre-spaceflight, back in the 18th century, when the invention of the telegraph allowed remote communication for the first time. AC took advantage of this new technology to set up a profitable business that employed couriers to deliver valuable items all over the world. At the time, the identity of the two founders - Messrs Armstrong and Cuthbert - was kept a closely-guarded secret; they were in fact women, a fact that did not become generally known until their deaths nearly a century later.
As humankind spread throughout the Solar System, so did AC, opening offices on all the main planets and some of the asteroids, and then as humankind discovered hyperspace travel, getting a foothold in other star systems.
At first, the company had little direct contact with their haulers, dealing with them via the comms. This lead to the rise of the new breed of cargo haulers, who rarely left their ships, just setting down on a landing pad to unload and load up again. But in recent years, the enhancements to remote communications technology have meant the facilities can no longer be trusted. Electronic communications can so easily be faked, which caused a huge rise in cargo hijacking. Conducting business face-to-face makes fraud and theft much easier to counter (at least, theft by haulers; the stevedores are another matter...), hence the requirement for you to actually show up at one of their offices to arrange the loading and unloading of goods! You can see the locations of the AC offices on the Sol planets by looking at the starter planet maps. On out-of-Sol planets, their offices are always on the landing pad.