Couriers are the highest stage a Runner can reach. Unlike them, they aren't just traveling between a few cities, but cross whole continents for their clients.
There are so few who manage to become one; not even a hundred are known on the whole continent of Issrysil.
A standard equipment for couriers is a gems that is enchanted with a [Detect Truth] spell, which prevents them from being deceived by people untruthfully proclaiming to be the rightful receivers of their delivery's.
Before a package is to be delivered by a courier, it is being enveloped in layers of some kind of brown canvas fabric, which is being bound by a black ribbon. At the center of said ribbon a runic stone is embedded, glowing with black light. That stone is the the Courier's Seal that is able to record the location, the face and identity of the recipient and the time when the the courier carried out his task.
That task is complete as soon as the Courier finds the owner of the package verifies his claim to it by using the gem that is enchanted with [Detect Truth], waiting for the owner to place his hand on the glowing Courier Seal, which upon touch loses his black light, becomes white and falls off the ribbon. 
- Getting [Double Step] and [Quick Movement] means that you've crossed two-thirds of the way of becoming a Courier.
- To become a Courier one has to be at least level 30.