As like the topic, may we have a Mail box and bank NPC on any tier Keep (top floor)?
I think if that available, people don't need to flight back to main city just gonna put somethings in bank or send items to alt/main toon. Like my Cultivating alt, I'm a healer with warband, I had many stabilizing need store into bank; normal I need to off warband then flight to main city... If there's a bank in keep, I guess people will not disagree to set this NPC (must be unattackable) stand on the corner, easy for people in/out stuffs.
Mail box is same as bank, it's just optional stuff for transfer loot chest or main/alt. There's an portal (live) at the edge of the top floor of keep, people can transfer from keep to tier warcamp. Now we don't have this services, if can set an mailbox there.
Just some advice suddenly popout in mind

Cheers!!