That part is confusing to me. I ran a fresh install of Django to confirm and it behaves as you suggest. Edit: Perhaps only for low digits. Hmm. >>> from

That part is confusing to me. I ran a fresh install of Django to confirm and it behaves as you suggest. Edit: Perhaps only for low digits. Hmm. >>> from django.core.validators import EmailValidator >>> e = EmailValidator() >>> e.__call__('foo@[1.2.3.4]') >>> e.__call__('foo@1.2.3.4') ValidationError: [u'Enter a valid email address.'] >>> e.__call__('foo@0.0.0.0') ValidationError: [u'Enter a valid email address.'] >>> e.__call__('foo@[0.0.0.0]') >>> e.__call__('foo@10.10.10.10') >>> e.__call__('foo@[10.10.10.10]') >>> e.__call__('foo@255.255.255.255') >>> e.__call__('foo@[255.255.255.255]')