To better understand how DKIM works, you can create a record manually. Various tools are available free of charge on the Internet, such as the DKIM Record Generator by EasyDMARC. At the top of the screen, enter a selector of your choice (such as k1) on the left and a domain on the right. The generator displays a private and a public key. The private key must be stored on the mail server (this can only be done by your email provider), and the public key is entered in the DKIM record.