contact form

If someone fill in the required fields in our contact form with a email like this ” (Email address hidden if logged out) ” we do not get the email.
Is this normal, because of security?

Our email field is marked as a required field.

We ask for it, because if someone do not want to fill in his email adress but he wants to get in contact with us only via telephone, he has to fill the email field. But if he fill it like above, we will never get it.