cant send mails from tool to outside domain users

Hi,

i have added a exchange 2013 email id with the tool. while replying from the tool, mail reaches to the internal domain(my domain) users. But getting error with outside users(other domains) ERROR: "Invalid address".

i have created connectors for the tool IP's and enabled everything from my exchange server but still facing the issue.

Kindly help me to resolve this issue ASAP

Thanks
Santhosh