DKIM key rotation is the process of updating your DKIM keys. You should rotate your keys periodically—the exact period isn't important, but the process itself is. It's a security measure that helps prevent attackers from impersonating your domain.

Meta: While DMARC protects you from a wide range of cyberattacks, it is no silver bullet. Here is a full list of which attacks does DMARC not protect you from!