In every city and most towns, there is a tall wooden building. The walls are studded with holes, and offer little protection from the weather. Countless birds can be seen flying to and fro, day and night, navigating around each other with effortless ease. Regardless of the climate, the birds in questions are abnormally large ravens, without fail.
The wooden structures lack a door - in fact, the entire lower third is simple a solid support from the rest of the towering building. The function is to act as another stop in the Conspiracy - the finest and fastest messaging service in all the land - or so the rumour goes. There are no human handlers to these birds, for they are not any beast - some ancient happening gifted them twice over - both the ability to speak in the tongues of humanoids and the intelligence to use it. Combining this with their natural gift of flight, they established themselves as a de-facto postal service, either physically carrying the message or relaying it by word-of-beak. This service is offered at decent rates, affordable to those who would have need of such a service, as well as rumours of the truly destitute being given free service when it matters most. Governments and armies throughout the land use the Conspiracy, as the fees are substantially less than hiring magical help.
However, the service is not as benign as it seems. The ravens are privy to much knowledge best kept in secret, and are all too willing to sell the information on to parties they can trust. If one were to discover the truth and attempt to spread it, the Conspiracy would quickly utilize their considerable monetary wealth to hire a 'trouble-shooter' before the damage became too great.
The birds themselves are about as varied as any race in temperament, bar that they are all fiercely loyal. General trends include protecting their less-intelligent kin and looking down their beaks at the bird-familiars of magic users. Furthermore, they do not get along with druids, finding their naturalist outlook haughty, boring and backwards. They are far more in-tune with the industrious races and cultures.
Prices should be left to DM discretion, with costs increasing as distance increases. Physical mail should be roughly 1.5x more than word-of-beak services, with maximum weights being no more than could be carried by two ravens holding a piece of string attached to the object.