Will soulbound items remain soulbound or will they be soulbound on equip?
I will share my thoughts with you:
I think, if we get the item by mail it will be soulbound on equip (that would be obvious), but if the items will "dropped" into the inventory of the particulary character the chance could be high that the item is already soulbound to this character.
Please don't rely on my post, but this is what I see as the most likely possibility.