ghpsitechek DMIK is not hard at all, but it can interfere with forwarding if thats all you do. Forwarding sends as you not the original sender, but some services will render it as the original sender just to make things look good, but it can cause problems sometimes.
DKIM is not required at all as long as you have the SPF records active.
Basically the server sending the message signs with a DKIM signature that the receiving server checks with the DKIM key you have in your DNS. But the real good rule is SPF that says who is allowed to send for your domain so at least get that working.