How can I send a confirmation Mail to the user who submits the form within the ContactForm Plugin ?
Apparently someone made a plugin that's doing exactly that https://straightupcraft.com/craft-plugins/contact-form-receipts
Make your own little plugin that listens to the plugin's
and sends the confirmation mail.
Just saw this, it is possible without building a plugin by hacking the standard contactform plugin. In the file contactformservive.php add:
$email->cc = array( array('name' => $message->fromName, 'email' => $message->replyTo) );
This will send an EXACT copy to the form submitter. It has one drawback that I noticed; the reply address is also the submitter, so if he/she wants to answer that mail it will return to him/herself. You could add a notion in the body with a standard reply address to prevent this.