Participants can contact the organizer of the event on the registration website. This opens up a popup where they can submit their request. To control who receive those:

1. Go to evenium.com 
2. Click My Events 
3. Click the name of the event under the I organize section. 
4. Click on the Configuration tab located on the purple bar 
5. Click Team Access
6. Click on any organizer/administrator and check or uncheck the Receive by email the participants questions/requests box.