May be you mistyped the email, when you are creating the form. Check that if is correct and still can't send, privately email me your login details so that I can ratify that for you.
You don't send email through your control panel, you send email through email account you created.
eg
www.thedomain.com/cpanel , a popup comes up you will type user: user@thedomain.com and password: whatever and click login, when you log in there is three methods of email applications there just choose any one and start sending email.
I most of the time use Roundcube.
I hope this helps, let me know if you have further question.
