To transport mail from that station using trucks, you need to build a truck station connected to it, and there are no roads next to that station so you can't do it... the only way with that setup would be to build a truck station on the tree at the top left of the station and then join it back to your road network around the top of the houses on the top left.
Normally in CB you get the bulk of your mail from other cities by rail, and then bolster it with some internal truck networks. See that loop to the left of the station? If you build a truck station at either end of it you can get a truck or two looping around and around delivering mail between them. Creative use of one-way arrows will also allow you to setup these "loops" on long stretches, eg "___>>[Station1]____[Station2]<<___" - once a truck goes in it can't get out and will transfer between the two stations forever.. just make sure both stations have "Mail" in both Supply and Accept.
I think the town layout is not very good - you can see this from the extremely high "CS" (Cycle Skip) count in the city window. This is how many times the city tried to build a house but had to start again after looping back on itself. In a perfect setup this is always 0, 53 is VERY high. See the 3-way junction under the "Reston (2737)" label? This is where the program starts each time it tries to build a house. It randomly chooses a direction then goes that way until it hits a junction, where it randomly chooses again. In your setup you can see that if it goes up, then 50% of the time it comes back because that road loops back to the "right" path. If it goes left, then 50% of the time it will come back due to the loop on the left (regardless of which way it goes at the first junction, the second junction has a 50% chance of sending it back). Finally, if it goes right then 50% of the time it will loop back via the "up" path, and when it doesn't do that, then 50% of the time it will turn left at the T-junction down the end and end up in the lake giving you a "HS" - House Skip. The big loops down the bottom are good in theory because they are long and provide ample space for new houses, but they are too hard to get to - half the time the house building algorithm loops back on itself or ends up in the lake! For comparison, the classic 2x2 or 3x3 square grid layouts will only loop back about 10% of the time.
Following on from the above, I would also recommend choosing a starting town with a 4-way main intersection, and never one that is blocked on one side by water (or mountain/industry etc.).