The auccion house and post box will increase inter player trade. The postbox need be just a facility to leave items at a station for another player to collect. And maybe a message service/email Communications left for off line players.
And auction house at capital stations.

Postbox: +1 really useful if you're selling something to someone but you need to logoff

Email: x=1 Useful for leaving a message to someone

Auction House: -1 you can already buy stuff from normal stations, what's the use of an auction house?

The corvus stations in sedina and bractus could hold an auction/sales houses/boxes with automated moths to drop the goods outside when the player is ready to pick them up.

The players would would dock and select the mission to launch a moth full of the goods they bought/won and drop it outside. Players would drop off the goods their as well with a mission leaving a certain number of an item for a player to pick up or be auctioned over a week.