Check the description, if it says "can't trade", it can't be mailed or added to your shared bank. If an item says "account bound" it can be added to your shared bank, but not mailed. If it doesn't say either, it can be mailed or added to your shared bank. If an item has been modded, it can't be mailed or added to your shared bank.
Some blue gear is tradeable, but not much. If it drops from a reward box or a boss it won't be tradable.
