Are you able to resolve the mx for the induvidual domains in the systems ?
Eg:-
In the system which is serving
www.aks.com
run
$ dig mx krish.com
this must give the ip address of the aks.com mail server.
and viceversa.
If this is not happening then i suspect you are using local DNS server whcih is not able to resolve the mx for the
interdomains but the external DNS are working fine !