It is a mandatory mention added in the framework of the GDPR rules and the CNIL’s French Data protection act.
This sentence allows people to stop receiving emails from this event. They will switch to "Opt-out" status on your guests database and they will no longer receive the emails.
If these participants wish to receive these emails again, you can contact the Evenium support (+33 1 47 70 90 35 / support@evenium.com) with a written proof of that wish so that we can change their status.