The Email Authentication feature allows website owners to sign emails through DomainKeys Identified Mail (DKIM). This allows the recipients of emails from the website owners domain to certify the messages sent from it are genuinely from the domain that they claim to be from. This works to prevent spammers from forging emails from your site.
Another feature of Email Authentication is the Sender Policy Framework (SPF). This allows a website owner to setup remote servers and IP addresses to send email from your domain. This helps minimize spam on outgoing messages.