A sender creates the DKIM by “signing” the email with a digital signature. This “signature” is located in the message’s header. The sending mail transfer agent (MTA) generates the signature by using an algorithm applied to the content of the signed fields. This algorithm creates a unique string of characters, or a “hash value.”

How Can I Test My DKIM?

You can also test DKIM by sending an email to a Gmail account. Open the email in the Gmail web app, click on the down arrow next to the “reply” button (top right of email), and select “show original.” In the original, if you see “signed-by: your domain name” then your DKIM signature is good.

How Can I Read the DKIM Header?

https://www.emailonacid.com/blog/article/email-development/what_is_dkim_everything_you_need_to_know_about_digital_signatures/

Worth Reading

https://www.smartertools.com/blog/2019/04/09-understanding-spf-dkim-dmarc