How is the lets-encrypt renewal process run?

Guys,

My MIAB is running fine, but I am wondering, what is it that automatically renews the lets-encrypt certificates? I didn’t see anything relevant in cron.

Look in /etc/cron.d/ and you’ll see some files, one is mailinabox-nightly

The cron mailinabox-nightly calls daily_tasks.sh which in turn calls ssl_certificates.py