Hi Thomas,
first of all, thanks to your post on this forum I was able to get my mailcow setup with Ciphermail up and running.
However, DKIM is still a topic. But I think the solution to the issue is, to add ARC validation capabilities to the gateway and then add appropriate headers to the encrypted/decrypted mails. I started a new topic for this: Discussion about whether it's possible to add ARC (Authenticated Received Chain) to the CipherMail Gateway - #2 by illebille