Email authentication helps to prevent spam. The options available in the Email Authentication tool in cPanel attempt to equip email messages with verifiable information so that the email server can automatically detect the nature of incoming and outgoing messages. Enable these features to reduce the number of failed delivery notifications you receive when spammers forge messages from your domains. These features also stop spammers who forge messages that claim to be from your domains.
DKIM allows your server to verify incoming email and prevent incoming spam messages. This feature ensures that incoming messages are unmodified and are genuinely from the indicated sender. To enable the use of DKIM for your domain names, click the Enable button.
The SPF system allows you to authorize servers and IP addresses to send mail from your domains. This feature prevents outgoing spam messages and to enable it just click the Enable button.
You can also modify the default SPF record via the tool. You can add additional A records and MX servers to be allowed, block specific IPs, manage the include SPF list and the "all" parameter of the record. You can find out more about the SPF record syntax in the official documentation.