diff --git a/users/forms.py b/users/forms.py
index 49135266..97fb3fc3 100644
--- a/users/forms.py
+++ b/users/forms.py
@@ -138,6 +138,12 @@ class UserCreationForm(FormRevMixin, forms.ModelForm):
         prefix = kwargs.pop('prefix', self.Meta.model.__name__)
         super(UserCreationForm, self).__init__(*args, prefix=prefix, **kwargs)
 
+    def clean_email(self):
+        if not OptionalUser.objects.first().local_email_domain in self.cleaned_data.get('email'):
+            return self.cleaned_data.get('email').lower()
+        else:
+            raise forms.ValidationError("You can't use an internal address as your external address.")
+
     class Meta:
         model = Adherent
         fields = ('pseudo', 'surname', 'email')
@@ -308,6 +314,12 @@ class AdherentForm(FormRevMixin, FieldPermissionFormMixin, ModelForm):
         self.fields['room'].empty_label = "Pas de chambre"
         self.fields['school'].empty_label = "Séléctionner un établissement"
 
+    def clean_email(self):
+        if not OptionalUser.objects.first().local_email_domain in self.cleaned_data.get('email'):
+            return self.cleaned_data.get('email').lower()
+        else:
+            raise forms.ValidationError("Vous ne pouvez pas utiliser une addresse {}".format(OptionalUser.objects.first().local_email_domain))
+
     class Meta:
         model = Adherent
         fields = [
@@ -323,6 +335,7 @@ class AdherentForm(FormRevMixin, FieldPermissionFormMixin, ModelForm):
             'gpg_fingerprint'
         ]
 
+
     def clean_telephone(self):
         """Verifie que le tel est présent si 'option est validée
         dans preferences"""
@@ -607,6 +620,9 @@ class EMailAddressForm(FormRevMixin, ModelForm):
         super(EMailAddressForm, self).__init__(*args, prefix=prefix, **kwargs)
         self.fields['local_part'].label = "Local part of the email"
         self.fields['local_part'].help_text = "Can't contain @"
+ 
+    def clean_local_part(self):
+        return self.cleaned_data.get('local_part').lower()
 
     class Meta:
         model = EMailAddress
@@ -631,6 +647,12 @@ class EmailSettingsForm(FormRevMixin, FieldPermissionFormMixin, ModelForm):
                 "Enable the use of the local email account"
             )
 
+    def clean_email(self):
+        if not OptionalUser.objects.first().local_email_domain in self.cleaned_data.get('email'):
+            return self.cleaned_data.get('email').lower()
+        else:
+            raise forms.ValidationError("Vous ne pouvez pas utiliser une addresse {}".format(OptionalUser.objects.first().local_email_domain))
+
     class Meta:
         model = User
         fields = ['email', 'local_email_redirect', 'local_email_enabled']