You have to create a daily cron to check digests to produce
0 4 * * * wget --http-user=zopescheduler --http-password=TrigOtad3 http://localhost:8080/mysite/@@digest-cron?maildigest-debug-mode=1 -O /dev/null
http://localhost:9880/mysite/@@digest-cron -O /dev/null
This add-on is tested using Travis CI. The current status of the add-on is :