Making postie work with cron jobs, fails with wp-config.php outside of web root

I use the excellent Postie plugin to post to this blog via email. I’ve been battling for days to get it to automatically check the mailbox for new message though, and while I still haven’t got it working using WP-Cron (WordPress’ “pseudo-cron”), I’ve finally managed to get it working via a direct cron job.

This is a companion discussion topic for the original entry at