Validate email fields

Closes #12215

modules/web_user/exceptions.py

@@ -0,0 +1,8 @@
+# This file is part of Tryton.  The COPYRIGHT file at the top level of
+# this repository contains the full copyright notices and license terms.
+
+from trytond.model.exceptions import ValidationError
+
+
+class UserValidationError(ValidationError):
+    pass