As you may or may not be aware, there are mail_admins and mail_manager functions, both take their lists from the settings file.

This is for mailing staff, based on is_staff being set on the user (I am assuming you have at least 1 all the time)

from django.core.mail import send_mass_mail
from django.conf import settings

subject = 'Comment added'
message = 'A new comment has been added'

mails = (
    (
        subject, 
        message, 
        settings.DEFAULT_FROM_EMAIL,
        [u.email]
    ) for u in User.objects.filter(is_staff=True)
)

send_mass_mail(mails)

I am using this in the save method on another site for comments, so myself and other staff are alerted of new and updated comments on the site.

If you wanted to create custom messages for each user, ie Dear Fred, I would suggest you keep to a simple for loop, it would be far less messy.