[deps] Migrate from django-celery-email to django-post-office #477

[Adityashandilya555]

Replaced archived django-celery-email with actively maintained django-post-office for async email handling.

• Updated requirements.txt: django-celery-email -> django-post-office
• Changed email backend configuration in Dockerfile
• Updated settings.py to use post_office app conditionally

Checklist

• I have read the OpenWISP Contributing Guidelines.
• I have manually tested the changes proposed in this pull request.

Reference to Existing Issue

Closes #477 .

Description of Changes

Migrated from the archived django-celery-email package to the actively maintained
django-post-office package. This ensures continued security updates and support for
asynchronous email functionality.

The migration maintains the same async email behavior while using a modern,
well-maintained package. All email configuration remains backward compatible.

Screenshot

[nemesifier]

@Adityashandilya555 can you please update this to be consistent with changes done in #521?

[nemesifier]

@Adityashandilya555 How did you test this to be confident emails are really sent?

This doesn't seem to be enough to me. Try the following on master:

docker compose logs postfix -f

In another terminal run:

docker compose run -it dashboard /bin/bash

python manage.py sendtestemail [email protected]

On master you'll see postfix activity trying to send email, likely failing because ISPs block email sending ports for preventing people from sending spam.

I tried this on this branch and nothing happens, it doesn't seem to send anything.

I believe we can switch to https://github.com/panevo/django-celery-email-reboot, which is a fork of the tool we've been using until now, which has proven to be simple and reliable.

[Adityashandilya555]

hi i have worked on this issue and created a new pull request for the same #524 Testing Method:

# Terminal 1
docker compose logs postfix -f

# Terminal 2
docker compose run --rm dashboard python manage.py sendtestemail [email protected]

Results:
The email pipeline is working correctly. Postfix logs show email activity:

postfix/smtpd[118]: 95C4120370E8: client=docker-openwisp-openvpn-1
postfix/cleanup[123]: 95C4120370E8: message-id=<176020434555.205.7616411433815178068@a45abb8efcb4>
postfix/qmgr[113]: 95C4120370E8: from=<[email protected]>, size=575, nrcpt=1 (queue active)
postfix/relay/smtp[124]: 95C4120370E8: to=<[email protected]>, relay=none, delay=31, status=deferred

[nemesifier]

@Adityashandilya555 next time you can simply force-push to the same branch to update the already open PR. Let's close this and continue in #524.