EmailBackend connection is not being closed

[wkleinheerenbrink]

When sending mails using the contrib.EmailNotifications package, the connection to the email backend is not being closed. Most EmailBackends will provide a fallback for this issue, but some don't.

In case of Django Naomi this results in the webbrowser not being opened to preview the created email.

Steps to reproduce:

1. Setup django forms
2. Choose django naomi as e-mail backend
3. Configure and send a form

No errors are thrown, but now browser will be opened too.

The connection is openened at:

aldryn-forms/aldryn_forms/contrib/email_notifications/cms_plugins.py

Line 173 in a53e751

connection.open()

The connection should be closed after this step:

aldryn-forms/aldryn_forms/contrib/email_notifications/cms_plugins.py

Line 195 in a53e751

connection.send_messages(emails)

More info on opening/closing connection:
https://docs.djangoproject.com/en/3.1/topics/email/#sending-multiple-emails