Exchange 2000 DNS

I have E2K on a DC at home…All Email works fine within mine and my ISP’s domain namespace(the ISP is supposed to be fowarding all mail to my server)..I can send email from inside my domain anywhere outside of my ISP domain namespace…but I cannotrecieve email from outside of my ISP domain namespace….the error message I get at the external Ex5.5 Server is DNS related…nothing on Technet.Please Help!Routing issues???