This is a great mod for transporting items smaller distances or larger ones.
It will work better at long distances if your friend is rendering the other mailbox.
Here is the showcase video: https://youtu.be/UeStibiBNHo
you can also do the /mail command for moderators to send items to mailboxes.
You can name mailboxes any name (Use a longer name for better encryption)
It might still be buggy due to it being made in a few hours. please contact me by commenting on my YouTube video if you find glitches.
the mod works on 1.18.2 and 1.16.5. Other versions are coming soon!