Mailbox Set Up
Important: You must have a mailbox sign in order to have a Nether Warp. Do not set your mailbox to any box except the nether warp mailbox that you plan to use for your Support Ticket. This is called "claiming your sign warp station".
These steps must be done in this order. Editing a sign afterwards will break the connection
Step 1: Find your corresponding sign in the post office. If you have the Bouncy 6 warp in the nether, find the B6 sign.
Step 2: Edit the sign (shift + right click) and replace "Your Name" with your Minecraft name
Step 3: Go to an unclaimed mailbox in the Subway that you want
Step 5: Go back to your sign in the post office
And voila! Now you have a super useful mailbox!
To send things to another player, have the item in your hand and right click the sign of the player that you want to send the item to. It will be removed from your inventory and placed in that player's chest.