Deprecated function: explode(): Passing null to parameter #2 ($string) of type string is deprecated in Drupal\sys\SendMail->envoyerEmailAvecTableau()

It's reading non existing config values, so the module needs a config schema and install config with defaults.

Then it tries to send an email on every page load, in sys_preprocess_page(). I think it should be doing it on cron instead.