We'll create fresh WordPress site with UTM tags + Landing page + "gclid" tracking for Contact Form 7 installed. You have 20 minutes to test the plugin after that site we'll be deleted.
This plugin will save UTM tags + Referrer (like google.com, etc) + landing (first page) to cookies on first user visit and on CF7 submit adds all info to mail body.
Please note that for security/privacy reasons, the Referer URL is stripped out when navigating from a HTTPS site to a HTTP site by the browser and in some other cases.
Setup: place [utm_and_referer] tag in the Admin email body – example
A UTM codes is a simple query variables that you can attach to a custom URL in order to track a source, medium, and campaign name. This allow you better understand from where visitors are coming and doing some actions (like submitting contact form).