I see that my colleague has replied in the ticket so I will post the reply here as well:
The mapping of the fields could not be empty, so in case you delete the Owner email field it automatically is mapped to its initial value.
In order to achieve the behavior you need, you could map the owner email field to another data. To show you this I have prepared for you a video demonstration. In that example the categories are empty and the e-mail field sent is empty. You could put there any other listed field.
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items