diff --git a/csharp/App/Backend/DataTypes/User.cs b/csharp/App/Backend/DataTypes/User.cs
index 7397eb6e2..77924b3de 100644
--- a/csharp/App/Backend/DataTypes/User.cs
+++ b/csharp/App/Backend/DataTypes/User.cs
@@ -4,6 +4,8 @@ namespace InnovEnergy.App.Backend.DataTypes;
 
 public class User : TreeNode
 {
+    
+    [Unique]
     public String  Email          { get; set; } = null!;
     public Boolean HasWriteAccess { get; set; } = false;
     public Boolean MustResetPassword { get; set; } = false;