Can't send email in management command run by cron - django

Question

I have a strange problem with a Django management command I am running via cron.
I've a production server set up to use Mailgun. I've a management command that simply sends an email:
from django.core.mail import send_mail
class Command(BaseCommand):
help = 'Send email'
def handle(self, *args, **options):
send_mail('Test email', 'Test content', 'noreply#example.com', ['me#example.com',], fail_silently=False)
This script works perfectly if I run it via the command line (I'm using virtualenvwrapper):
> workon myapp
> python manage.py do_command
or directly:
> /home/user/.venvs/project/bin/python /home/user/project/manage.py do_command
But when I set it up with cron (crontab -e):
*/1 * * * * /home/user/.venvs/project/bin/python /home/user/project/manage.py do_command
The script runs (without error), but the email isn't sent.
What could be going on?

Answer 1

OK, the issue was that the wrong DJANGO_SETTINGS_MODULE env var was set and there were a few things throwing me off the scent:
My manage.py script defaults to the "development" version of my settings: settings.local and this uses the command line email backend. Cron suppresses all output so I wasn't seeing that happening.
Secondly, I was testing in a shell that already has DJANGO_SETTINGS_MODULE set to settings.production, so it appeared that the script ran correctly when I ran it on the command line.
The fix is easy, add DJANGO_SETTINGS_MODULE to the crontab:
DJANGO_SETTINGS_MODULE=config.settings.production
*/1 * * * * ...