Regional Bureau of Communications Office

In every society, the flow of communications is deeply important. In a society built around the arcane, this is no different. Thus, the Bureau of Communications was established in order to facilitate quick and easy transit of mail and small packages across the multi-continental span of the Dominion. When initially developed, the Arcane Mirror was a niche curiosity, useful only for moving small objects from place to place. Its properties as a portal were disappointedly lacking, as living beings that attempted to cross its threshold were subjected to severe warping, burns, and usually outright death. But it was eventually found that objects such as notes or small packages could be sent incredibly vast distances with little to no effort, and this quickly revolutionized the flow of information, governmental organization, and infrastructure development. As mirrors only had one point of attachment, a series of increasingly centralized bureaus would have to be established, full of clerks, administrators, and golems to run and operate them.
Each village or collection of villages of over 1,000 persons would be assigned a mirror, an area code, and a regional seal to denote letters from the area. 
Towns of over 10,000 residents may have multiple mirror offices using the same a rea code designated to them.
Large cities may be split into multiple 'district' sub-codes, and also have 'regional' offices tasked with holding a number of mirrors from across their region's towns and villages to ease burden on the central bureau. 
Likewise, the capital of each Duchy in the Dominion would be home to much larger office centers teeming with bureaucrats and coordinators moving mail up and down the ladder.

Arcane Hand Mirrors are almost entirely seen being used by ambassadors, military officers, and the military branch of the Communications bureau, and have less complex bureaucratic ladders attached to them, usually being direct lines to their higher ups.

The prospect of privately owned arcane mirrors is one only the most affluent can enjoy, as they require a lot of power, ample maintenance, and safety precautions to own and operate. The vast majority of mirrors are owned, operated, and manufactured by the Bureau of Communications, who answer only to the Duchy & Empress herself.

The Establishment of the Bureau has been claimed to have stifled development of the communications sector, as the ease of sending mail across continents within a day means things such as the Telegraph or fax machine would be not nearly as necessary or novel as in our world.