Hello,
We have checked out your Codes and it has several errors. To include your Custom Form Fields inside the Form, make sure that the Form Inputs name Attribute is properly configured and matches the prefix defined in your Form. Example: name="mutuoRiassunto" should be replaced with name="template-contactform-mutuoRiassunto" . This would be applicable for all the Form Inputs. Additionally, we have also noticed that your Form is using include/sendemail.php which is not valid anymore. The Latest Version of Canvas uses include/form.php File. Make sure that you follow the Documentation > Forms Section for complete instructions on how to use Forms.
This will definitely fix your issues. Hope this Helps!
Let us know if we can help you with anything else or if you find any further issues.