When you setup a custom domain email and forward it thorugh KaiMail, it DOES break DKIM of the sender since we're adding headers, through our own custom headers and the hops. The question is: Will it matter within the scheme of email authentication?
The key point here is ARC (Authenticated Received Chain) sealing: This is usually the hardest part of email forwarding. When we send out the email, we sign it with our own key for DKIM and then also sign it for ARC. From the recipient's point of view, the email is authenticated, is not tampered with along the way and was proven to originate from where it says it came from. You can read more about ARC on our blog here.
