enforce email address uniqness

shellvalier/wsgi.py

@@ -10,7 +10,10 @@ https://docs.djangoproject.com/en/2.1/howto/deployment/wsgi/
 import os
 
 from django.core.wsgi import get_wsgi_application
+from django.contrib.auth.models import User
 
 os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'shellvalier.settings')
 
 application = get_wsgi_application()
+
+User._meta.get_field('email')._unique = True