dedicated mailserver issue

okay i changed the server domain name and email now works correctly. my last questions is

now that i have an external email server and set all of my co-domains to external email. is there a way to allow relaying to domains listed in my domain tables? this way i do not have to ad MX entries to all of my co domains? if i try to send an email to a co domain i get relay access denied. but if i add an mx entry to the co domain DNS it works. i have over a hundred domains to go through and just looking for an easier way to work this out.

if it helps the server is on the same network so if i could maybe relay to only the same subnet or ip address...

 

You must enable "Server requires authentication." in your email client.