Player events + mail receive event

src/main/java/emu/grasscutter/server/event/player/PlayerReceiveMailEvent.java

@@ -0,0 +1,24 @@
+package emu.grasscutter.server.event.player;
+
+import emu.grasscutter.game.mail.Mail;
+import emu.grasscutter.game.player.Player;
+import emu.grasscutter.server.event.Cancellable;
+import emu.grasscutter.server.event.types.PlayerEvent;
+
+public final class PlayerReceiveMailEvent extends PlayerEvent implements Cancellable {
+    private Mail message;
+    
+    public PlayerReceiveMailEvent(Player player, Mail message) {
+        super(player);
+        
+        this.message = message;
+    }
+    
+    public void setMessage(Mail message) {
+        this.message = message;
+    }
+    
+    public Mail getMessage() {
+        return this.message;
+    }
+}

src/main/java/emu/grasscutter/server/event/types/PlayerEvent.java

@@ -0,0 +1,19 @@
+package emu.grasscutter.server.event.types;
+
+import emu.grasscutter.game.player.Player;
+import emu.grasscutter.server.event.Event;
+
+/**
+ * An event that is related to player interactions.
+ */
+public abstract class PlayerEvent extends Event {
+    protected final Player player;
+
+    public PlayerEvent(Player player) {
+        this.player = player;
+    }
+
+    public Player getPlayer() {
+        return this.player;
+    }
+}