Because of the prevalence of Teleportation Circles, someone figured out that delivering messages in bulk would be smart, on account of the tolls on travel. This started as a grass-root movement, but soon became SUCH AN IMPORTANT AND COMPLICATED THING. That there had to be developed a system. Following this character-codes were developed for cities and settlements, roads were named and numbered in larger settlements, were not everyone knows each other. Postage is paid on delivery. It is split between the messenger and the receiver. If passed on it is split in two again. Being the first in line is therefore encouraged, and mail men therefore are motivated to encourage the sending of mail in their local settlements.
Mail men often operate in pairs, one stays behind and takes postage, while the other leaves on 1-3 day trips on a “route” usually through 1-3 portals.