[exim] DMARC DKIM ?????

OK so my server hosts several domains. I have successfully setup DKIM
and everyone is passing using the main server as the outgoing SMTP.
The problem I am having is that the DMARC fails for all domains but the
main server.
What I want to do is send from main.server.com and have
user@??? pass the DMARC and all searches have failed for a
simple fix for a simple idiot. Everything found is for Debian and
others. I have tried some to no satisfaction.
I am running Exim 4.80.1, Dovecot on SUSE 12.3 I am at wits end can
anyone shed some light or suggest a how to to make this work? (or even a
good tut for a dummy's "R" us)

Thanks