Add setting for message retention

[joshuadavidthomas]

Since we are saving the entire email, including any attachments, in a database table, there is potential for the space to grow and grow unless there is some sort of way to clear out old emails.

I think there should be a new setting, something like MESSAGES_RETENTION_SECONDS that takes an int of the number of seconds to keep messages. Then somewhere in the relay loop, either within the runrelay management command, the send_all function, or maybe a new function that is called from within runrelay, that filter's all messages by created_at__lt=timezone.now() - app_settings.MESSAGES_RETENTION_SECONDS and deletes any found.

[jefftriplett]

If the goal is for runrelay to be the primary service, then it might make sense to call a cleanup task/function from there.

Not to overcomplicate it, but I could see someone wanting messages to immediately delete after successfully sent, and I could see people wanting to store the last n-messages for anyone who might send 1000s a day.

[joshuadavidthomas]

# email_relay/conf.py

# keep all (default)
MESSAGES_RETENTION_SECONDS = None
# or
# delete after sending
MESSAGES_RETENTION_SECONDS = 0
# or
# delete after a week
MESSAGES_RETENTION_SECONDS = 604800

Then in the runrelay:

# email_relay/management/commands/runrelay.py
...
send_all()

if app_settings.MESSAGES_RETENTION_SECONDS:
    if app_settings.MESSAGES_RETENTION_SECONDS == 0:
        Messages.objects.sent().delete()
    else:
        Messages.objects.sent_before(timezone.now() - app_settings.MESSAGES_RETENTION_SECONDS).delete()

Then for the n messages, something like:

# email_relay/conf.py

# keep all (default)
MESSAGES_SENT_MAX_KEEP = None
# keep the last 1000
MESSAGES_SENT_MAX_KEEP = 1000

Not in love with that setting name, but I don't hate it so it'll do for now, unless something better comes up.

Then:

# email_relay/runrelay.py
...
send_all()
...

if app_settings.MESSAGES_SENT_MAX_KEEP:
    # do the slicing and dicing here