'Normalize the address by lowercasing the domain part of the email
address.'

@classmethod
def normalize_email(cls, email):

    email = (email or u'')
    try:
        (email_name, domain_part) = email.strip().rsplit(u'@', 1)
    except ValueError:
        pass
    else:
        email = u'@'.join([email_name, domain_part.lower()])
    return email
