Hi, we have a web appliation with its smtp service to send notification email out once an online booking is done. recently we got this issue, all external emails address can receive email from it except of 2 internal domains. these 2 are on exchange 2003. any advice where to check? thanks

How is the web application configured to send out emails for internal and external domains? Is it to an Exchange server or any other relay server? You may have to have a receive connector setup on Exchange server to receive the emails from that application.