from django.core.mail import send_mail
from django.db.models.signals import post_save, pre_save

def create_thumbnail(sender, instance, **kwargs):
    send_mail('pre', 'Here is the message.', None,  ['mail@mail.com'], fail_silently=False)

pre_save.connect(create_thumbnail, sender=New)

def create_thumbnail(sender, instance, **kwargs):
    send_mail('before', 'Here is the message.', None,  ['mail@mail.com'], fail_silently=False)

post_save.connect(create_thumbnail, sender=New)