Cannot set sender address for emails, which is disallowed by my email provider

[snowhunter]

Steps to Reproduce

Tested with RESET PASSWORD functionality in stock Docker image

1. Use an email provider that requires a valid from address to send. I used Gandi for this.
2. On home page, select "FORGOT PASSWORD"
3. Wait for request to fail and 504 error to be displayed.

Expected results:

An email sent to me, and a success message on the page

Actual results:
504 page is displayed.

The stack trace displayed on the page is below.

Logs

SMTPRecipientsRefused at /en/user/password/reset/

Request Method:	POST
http://wger.my-domain.uk/en/user/password/reset/
3.1.8
SMTPRecipientsRefused
{'mail@email.me': (504, b'5.5.2 webmaster@localhost: Sender address rejected: need fully-qualified address')}
/usr/lib/python3.8/smtplib.py, line 885, in sendmail
/usr/bin/python3
3.8.5
['/usr/local/bin', '/usr/lib/python38.zip', '/usr/lib/python3.8', '/usr/lib/python3.8/lib-dynload', '/usr/local/lib/python3.8/dist-packages', '/home/wger/src', '/usr/lib/python3/dist-packages']
Mon, 12 Apr 2021 08:48:10 +0100

Have set the following environment variables in the prod.env file without success.
FROM_EMAIL - As per Discord
EMAIL_FROM - As per python3 manage.py diffsettings |grep EMAIL and seeing an EMAIL_FROM field
DEFAULT_FROM_EMAIL - As per Django https://docs.djangoproject.com/en/3.1/ref/settings/#std:setting-DEFAULT_FROM_EMAIL

[rolandgeider]

TODO: check that everywhere where we send emails, the FROM address is correctly set (and document how to configure it)

[rolandgeider]

This should be fixed in master but currently there's a problem with our github actions for docker and no new images can be built