Granted the mail slot is small and its been like that since the very beginning of Elite, but can't there be some improvement added the mail slot, make it bigger or other. Why not add a CG for referb the mail slot on the station, we deliver the resource needed to work on the mail slot.
Just an idea and yes it will take time, this is how game should progress in time for improvement.
"Well it's like this, you see we built this station, cost us 100t credits, a million people live in it, we designed it for the ships of the time, we didn't imagine ships getting so large, but now we can't kick out a million people, where are we going to put them for a start, and redesigning the letterbox to take larger ships means completely dismantling the station, have you any idea how much that is going to cost and how long it's going to take. And that's without doing the same to every other station in the system!"
You see I don't think we should just try and retrofit all the old stations, you would never do it in real life, and yes I know it's just a game, but I like my universe to be consistent, even if it is just a game. The Panama Canal is an example of this in real life, the old canal locks are to small for the new ships, some of those things are HUGE, but they don't just rip out the old dock, that would disrupt traffic for decades and cause no end of problems, so they built a series of parallel locks and new canal.
So new stations could maybe have the new larger slots, old stations stick with what they have and pilots of big ships either take a bit more care docking, or fly smaller ships into the stations with smaller slots if they can't handle it the way it is.
Oh yes, the mail slot isn't really small, your flying a frigate sized ship, everything looks small!