Yes, as long as they are on same server you can mail anything that is not bound to you to an alt.

Can you transfer items from one character to another in BDO?

Item Copy can be accessed via the Tag Character system and will let two characters share a limited amount of gear. The function will be available to characters level 56 and above once they’ve successfully completed the “Marni’s Suspicious Device” questline.

Can you share mounts between characters BDO?

You can store your items in each of the city storages so your other characters can access and use those items too. Your horses, donkeys and carts are also shared, but only if they are in the stable.