It's true we haven't really gotten an official answer on it, but if you want to know what the community thoughts are, there's been some discussion here:
https://www.pantheonmmo.com/content/forums/topic/5811/mail-how-should-it-be-handled
https://www.pantheonmmo.com/content/forums/topic/7285/social-gatherings-instantanious-postal
https://www.pantheonmmo.com/content/forums/topic/5785/shared-bank-system/view/page/1
And just type "auction" into the search function to pull up a litany of threads about how in-game item trading can be handled.