Well, aside from the taxi stand, it seems kind of odd that they would have the mail sorted directly in the station.
I don't think they did that, but depending where they were going, on short trips they were either already sorted and just loaded on board or on longer trips sorted on route (like on Titanic).
I could be wrong about the "Cab Road" use for mail (at the time in 1912) as photos that showed mail vans or trays seemed to date from the 1930's onwards after the station was taken over by Southern.
I have seen other photos of the "Cab Road" also used for queuing as people went on day excursions or trips to Ascot.
(Date Of Photo Unknown)