Address Tag is a craftable item used for specifying the recipient address on a mailable item.
It's also used to change address of a mailbox.

Usage

Address selection

Using the item in hand will open interface where player can input an address.
Interface will show autocomplete suggestions, which can be selected with mouse or arrow keys and applied by pressing [Tab].

Info

Pressing [Ctrl] will toggle the suggestions box, and will show all known addresses when input box is empty.

Address Tag interface

Application

Address tag is applied to a mailable item by picking it up in inventory and right-clicking with it on the target item, similar to a bundle.
Alternatively, address tag can be applied by crafting it together with mailable item.

Tag is consumed in the process.

Changing mailbox address

Using it on the mailbox will open the same interface that can be seen when placing a mailbox, allowing its address to be changed without breaking the block.