In Kerio you can easily enable DKIM.
- Go to the domain name settings.
- Tick that you want to do DKIM
- Put the generated public key in the DNS.
It may take a while for Kerio Connect to see the DNS change and will give a notification. Please check again tomorrow.
When this message is gone, all outgoing messages are provided with a signature in the header so the recipient can check that you are actually allowed to mail from that domain name.