I am having a problem with our Exchange 2010 and Exchange 2003 coexistence. Our exchange 2003 server has been in place working perfectly. I just added a Exchange 2010 server to the domain. I added one test mailbox . I can send email internally to a 2003 mailbox and externally to yahoo account but can’t receive email into the test mailbox(2010) both internally from a 2003 mailbox or externally.