To activate the confirmation email in the contact form on inCMS, you need to set up reCAPTCHA. On the Google platform, you can enable reCAPTCHA

reCAPTCHA uses an advanced risk analysis engine and adaptive challenges to stop malicious software from abusing your website:

Enter your domain and get two API keys: the Site Key and the Secret Key! First, copy the Site Key and paste it into inCMS under the Settings in the Site Key section. Then copy the Secret Key from Google reCAPTCHA and paste it in the settings under APIs, but this time under Secret Key.  Save the settings and close the window. Now you can activate the reCAPTCHA checkbox in the contact form on inCMS. Then click on "Save" and close the window again. Afterwards, you can also activate and save the checkbox for the email confirmation.