Configure staging to greylist outgoing mail

[Paul Everitt]

According to Flying Circus (FC), our outgoing mail is getting a spam score due to using port 25. Switching to port 587 means TLS and a username/password. Instead, we can use their system to whitelist KARL for mailing:

"""
Greylisting
By default external mail servers have to pass greylisting when delivering mail for the first time. Service users may whitelist specific clients or recipients by setting a whiteliste rule in /etc/postfix/postgrey_whitelist_clients.local or /etc/postfix/postgrey_whitelist_recipients.local as described on the postgrey man page.

To put changes into effect, invoke sudo /etc/init.d/postgrey restart as service user.
"""

For this ticket:

- Research this topic
- Add yourself to KARL's etc/whitelist on karlstaging10/11 and restart
- Generate an email from KARL to you and inspect the headers spam score
- Perhaps also watch /var/log/mail to see what it reports
- Follow the gentoo instructions above and repeat
- See if it affects the spam score

If it works, then we'll discuss doing it in production.