Domain Keys Identified Mail (DKIM) is a mechanism that allows authentication of the origin and content of email messages. It’s a free technology used to trace a piece of email back to the domain that sent it. An email will be signed using a private domain key when it is sent It is checked by using a public key stored within the DNS on the receiving mail server. It allows the user to assess whether the context of the message has been changed during its transmission. 

It prohibits an attacker from manipulating the message before it hits the intended recipients. DKIM signatures will withstand routing, making it preferable to SPF and a great way to protect your address.

This authenticates the identity of the recipient using public key (asymmetric) cryptography ,RSA digital signatures.