I'm using Exim to relay emails to an smtp_relay. The problem is if the user exists and has an email address it won't exit the server and send them mail using our relay. I need it to go to the relay even if it's an internal email address. How do I accomplish this?
When Exim sends mail, it uses /etc/localdomains file to determine the route - either outbound (if the target domain is not in localdomains) or local delivery (if it is). So, the solution would be to remove the target domains from the /etc/localdomains file.
However, don't edit that file directly because every edit to a locally hosted DNS zone will overwrite the localdomains with new values. Instead edit the DNS zone.