I understand the concerns regarding obliviating the importance of mailbox size, so I submit this as an addition to at least remove the hassle put on sending to smaller mailboxes
shipping boxes
wooden box = 50
strong wooden box = 150
treasure chest = 500
red trunk = 1500
you an combine them with their full quantity of a single mailable item, which you can in turn send as a single box; you must have a mailbox that is equal to or larger than the box you'd like to create
this lessens the hassle on so much of trade, larger mailboxes can resolve 100k transfers in a few clicks, but still send a new player a gift of 1k OJ without setting aside 30+ minutes for it.
this will then incentivize players to increase mailbox size more, as it's usefulness rises to meet the cost.
this may start the incentive for even large mailbox players to keep increasing as new, larger, boxes are added.
