Is this happning for any specific domain or for every domain mail ?

For this kind of error there is multiple disscussion open in this forum, pls check if you get any solution from that.

And for troubleshooting purpose pls put MTA in debug mode and flush your delivery queue for 2 to 3 min and revert back changes done for logging.

and check for "maillog" for communication detail to find our  whts happning.

Has anyone used the new symantec Multitier. I just want to know about its perfomance

HI,

I have even faced the same problem & resolved, kindly follow the below step and try.

Go to administration-->configuration-->SMTP-->Advanced-->change "non-local delivery" & "dynamically routed message" from "auto" to out going interface IP address.

Regards,
Laeek