Email spoofing is the forgery of an email header so that the message appears to have originated from someone or somewhere other than the actual source. Email spoofing is a tactic used in phishing and spam campaigns because people are more likely to open an email when they think it has been sent by a legitimate source. The goal of email spoofing is to get recipients to open, and possibly even respond to, a solicitation.
If you want to test your own domains exposure to mail spoofing, please (1) enter the domain name (example.com) and a (2) email address associated with the same domain (e.g. firstname.lastname@example.org) and press run. You will see the results at the bottom (3).