Improve Email Security with Redesigned DKIM Keys
Where: This change applies to Lightning Experience, Salesforce Classic, and all versions of the Salesforce app in all editions.
How: Enable this critical update to improve security and make it easier to create and maintain DKIM keys. From Setup, enter Critical Updates in the Quick Find box. Then select Critical Updates. For Enable Redesigned DomainKeys Identified Mail (DKIM) Key Feature with Increased Email Security, click Activate.