Earlier this year I made a mailbox system. You can view this post here if you wish to see more information on it. Mailbox System - Send mail to users offline or in another server. (SHOWCASE) - Help and Feedback / Creations Feedback - DevForum | Roblox
But since I made this, I haven’t tried to improve it and it’s basically just been sitting collecting dust. Thought I’d open it for anyone who would like to use it/learn to make something like it. It’s horribly optimized, but the core function is there.
Basically in order to send messages to people they have to have joined the game before so it can make data for them. After it makes the data the user can be offline or in another server and it will successfully send messages to them. Credit in games is not needed, however the mailbox/meshes in that game are from a free mesh website called sketchfab. So be cautious using it in an actual game.
Mailbox Workshop - Roblox