Send email from a post

Hi guys, I would like that in the specific post posted by a user, the visitor interested in the ad could contact him by email. Just that I want everything to be on the same page, I do not want a page to send mail, but in the same post.

https://www.codeigniter.com/user_guide/l...il-library

PHP Code:

public function view($id = null) {
        $data['itemView'] = $this->items_model->getItem($id);
        if (empty($data['itemView'])) {
            show_404();
        }
        $this->load->view('themes/header', $data);
        $this->load->view('items/view', $data);
        $this->load->view('themes/footer');
    } 


This is the View function in the controller, what should I do?