I have configured a intranet mail server for a domain like testsite.com in my LAN and this domain is hosted in a (internet) server testisp.com which runs my domain testsite.com as a vitualhost in exim.My LAN clients are using intrantnet mail server so if mail is send for a testsite.com then mail is relayed locally.

Now the issue is some of our office empolyees who have mailids in domain testsite.com are out side of our LAN and not able to use intranet server,so if our office employess inside LAN are sending mail to those are outside the LAN then it stored locally and not send to the main server hosted in testisp.com.How can i forward mail to testisp.com for certain mailids ?

Thanks in advance...