There's a living information economy in Skyrim on Aurbis, there's no open PM system, there are messages scribbled onto notes or text written into books or ledgers by scribes, which are then transferred to messengers and delivered by hand. But not everyone who gets their hands on your messages will be able to read it: Literacy is a skill and now a part of the Speech skill tree. Scribes and messengers will be essential for any working operations.
More to come — the Literacy skill tree, how scribes work, courier guilds, and the ways a message can be intercepted, copied, forged, or destroyed.
