If you have your mailinabox installation behind HTTP reverse proxy, such as nginx proxy manager for example, mailinabox will send you emails each day with subject TLS Certificate Provisioning Result, containing errors.

That’s because it fails to install let’s encrypt certificates. Your web certificates are handled by your reverse proxy, so you don’t need mailinabox to do that. To disable certificate provisioning, open file:
/root/mailinabox/management/daily_tasks.sh and comment out this line:

management/ssl_certificates.py -q 2>&1 | management/email_administrator.py “TLS Certificate Provisioning Result”

Restart service:

systemctl restart mailinabox