We really do need a mailbox function, if only for ease of trading materials. If someone I know wants a certain material that I have, we have to go meet up in a city if they're online and if they're not I'm stuck holding it until we can both meet up. It could also be a small gilsink, just require a small fee for delivery maybe scaling in relation to the item.

Honestly it's a luxury feature and can wait until after the battle updates but it is a feature that would make things go much more smoothly.