DomainKeys Identified Mail (DKIM) is an authentication system used to verify that an e-mail has been sent by an authorized server or individual. An e-signature is added to the header of the email by using a private key. When the email message is received, a public key that is available in the global Domain Name System is used to verify who exactly sent it and if the content has been modified in some way. The primary function of DKIM is to block the widely spread scam and spam email messages, as it makes it impossible to fake an email address. If a message is sent from an address claiming to belong to your bank, for example, but the signature doesn’t match, you will either not receive the email at all, or you will receive it with a warning that most likely it is not genuine. It depends on mail service providers what exactly will happen with an email that fails the signature test. DomainKeys Identified Mail will also offer you an extra layer of security when you communicate with your business associates, for instance, since they can see for themselves that all the emails that you send are legitimate and haven’t been tampered with in the meantime.