mailbox is made to work as a crosswalk module. All you need to do to use mailbox is to put it inside the server modules folder where crosswalk expects them. Then, you can start using mailbox functions through any other crosswalk server modules.
You can download the Roblox model file and insert it directly into your game.
As a Git Submodule¶
To add the project as a git submodule into an existing git repository, run:
git submodule add https://gitlab.com/seaofvoices/mailbox.git modules/mailbox
This will insert it in a folder named
modules under the root of the repository, but you can put it anywhere you want. Then, you can use a tool like Rojo to sync the code into your place.