Easy Forms automatically detects the IP addresses of users submitting forms. You can find this info on the Submission Manager of your form by clicking on each individual submission.
You may to insert these IP addresses into the Notification or Confirmation emails. To do so, in the Message content, you need to enter the {{ip_address}} placeholder. The placeholder will be replaced with the IP address of the person submitting your form.
You can also insert variable code, including the IP Address into the Subject Line of the Notification or Confirmation email by using the same technique.