Form plugins, email configuration

I can't find how to configure the mail address for the Form plugin...
I've got this error message :
Cannot send message without a sender address

Where could I configure it please ?

do you have the email plugin configured correctly ?
if not, this is the problem.

In Admin Panel -- Plugins -- Email -- Email Defaults -- From/To fill in your Email Address.

Thanks, with Email, it's better ;-)
But I have a new pbm now...

Display page not found. Please check the page exists.
I can't find where to configure the page after the form is sent...