You might get an error message like this when you're using Google Business G Suite for your company email, and you receive an enquiry from your website which uses the same domain name (eg mycompany.com).

This is because Google thinks that all emails from your domain name (eg @mycompany.com) should be coming from itself (from G Suite) and not from your website. The error itself is a false positive, and in this scenario can be safely ignored. So just press the "Looks safe" button.