Send an email once object meets certain criteria

Question

[Hopefully I entitled this post correctly]

I have a (sort of) 'follow' twitter thing going on. Users can follow a company profile object, which creates a follower object.

class Follower(models.Model):
    created = models.DateTimeField(auto_now_add=True)
    modified = models.DateTimeField(auto_now=True)
    profile = models.ForeignKey(UserProfile)
    company = models.ForeignKey(Company)
    verified = models.BooleanField(default=False)
    from_user = models.BooleanField(default=False)

...

class Company(models.Model):
    owner = models.ForeignKey(User, null=True, blank=True, on_delete=models.SET_NULL)
    name = models.CharField(max_length=200)
    ... and more fields that aren't relevant

What I'd like to do is send an update email to the company profile owner, after 5 new followers. 'You have 5 new followers!'.

As of right now I'm sending an email to the owner every time they get a new follower. A little much, I know.

I'm guessing I need to create a list of followers, send it, and then delete it to prepare for 5 new followers? I'm really not sure how to go about this. Any help or suggestions are greatly appreciated.

view:

@login_required
# this is creating a follower. Maybe I shouldn't send the email through this?
def follow(request, id):
    company = Company.objects.get(id=id)
    profile = get_object_or_404(UserProfile, user__username=request.user.username)
    try:
        follower = Follower.objects.get(profile=profile, company=company)
        if not follower.verified:
            follower.verified = True
            follower.save() 
        messages.success(request, 'Now following %s\''%company.name)
        mes = Message(subject="New Follower", sender=profile, recipient=company.owner)
        mes.body = render_to_string('emails/email-message/new_follower.html', RequestContext(request, {
        'sender': profile,
        'receiver': company.owner,
        }))
    except ObjectDoesNotExist:
        messages.error(request, 'Failed to follow.')

Answer 1

Send the email every time the number of followers for a specific company becomes a multiple of 5, like so:

   if not (Follower.objects.filter(company=company).count() % 5):
        #send the email