@Tsoo cross world mail, and cross town mail will surely not exist. Fractured is all about travelling with your goods and risking the travel dangers for better profits.
Cross town mail system would just be going around that, and I can tell you with pretty high certainty that we will not see that.
Intra- city mail with COD, like a local cargo bay, where you could leave your item with COD, for buyer to come pick up on the spot where you left it and then pay for it could be interesting.
Something like this we already will have (market stands to sell your goods). Just the reservation system wasn't mentioned (unless I'm mistaken), but it would likely be easy enough to implement.
So reservation system tied to market stands, I can see that.
Normal market stand with all the items you placed on it, but as an extra option you reserve item X, for person Y, with price tag Z, for time duration T, and if this person fails to come pick it up in designated time frame, then this item just transfers to your general item assortment on market stand and becomes available for anyone to buy at designated price tag.