Your problem lies here. The @ in your domainlist is expanded to the value of
the primary_hostname setting, or the machine's own host as determined by
exim when primary_hostname is not set. For this reason, your domainlist
contains only subdomains and the primary host. The domain
redoakhealthcare.com is not on the list, and thus your server will think it
isn't a local domain, and deny relaying, since outside hosts are not on its
relay list, and redoakhealthcare.com is not on its relay_to_domains list.
Here is the solution to your problem, and a much simpler (faster) way of
doing the whole domain list (with sub domains):