Store whether we know email addresses are working because links have been clicked

src/pretix/control/forms/orders.py

@@ -340,7 +340,7 @@ class OrderContactForm(forms.ModelForm):
 
     class Meta:
         model = Order
-        fields = ['email']
+        fields = ['email', 'email_known_to_work']
 
 
 class OrderLocaleForm(forms.ModelForm):