Domain Keys Identified Mail (DKIM) is another method of e-mail authentication. This method uses information about domain which is published by the domain owner. That information allows the receiving server to verify if the e-mail message was sent by an authorized owner of that domain name.
To enable SPF and DKIM:
1) Login to your cPanel account.
2) Scroll down and select the ‘Authentication icon’ from the section "E-mail".
3) Here you can see the options to enable SPF and DKIM records. Click "Enable" and the records will be added to the DNS zone.