I want to set a message that each player sees whenever they join the server. I don’t want to change the join or leave message (e.g., “<player> has joined the game.”) Rather, I want to set a message that a player sees when they join the server (and not just for the first time). Only the player joining will see this message. I searched for “join message” plugins, but I keep finding plugins that change the join/leave message, which is not what I want.
MOTD; there should be a file in the Essentials plugin folder called motd.txt. You'll probably have to give your players the permission (essentials.motd) to see it though.