External Email Issue

Cannot receive external emails in a domain on Exchange Server 2003

I cannot receive external emails in one of two domains on Exchange Server 2003. What could it be?

External Mails are not getting to HUB server, it remains in the Queue in Edge Server

Error in Edge Server: MSExchnagemailSubmission not found MSExchnagemailSubmission Service on server edge was not found to be installed Error executing test-MAPI connectivity HUB server : its a donian server with all reqired roles and features installed.DNS configured, can resolve edge server....

SBS 2003 / Exchange internal email issue

We got a SBS2003 installed and it comes with its own exchange. We have set it up for internal emails and for external emails, we’ve a smart host at our ISP. So whenever someone email to someone inside office, it goes to exchange, exchange recognized it as internal email and does not send it out...