Unable to receive emails to exchange on a SBS 2003

Hi I have a SBS set up behind a NETGEAR WGR614 router. I can’t get a static IP with my ISP, so I signed up with DYNDNS to host my external Domain Name.

I can send emails via my exchange to the outside world but I can’t receive back from anything.

Have tested the SMTP port via nwtools web site and the connection times out.

All the ports have been enabled on the router.

I can access OWA externally from the network, and have tested that I can send OK, but it still won’t receive.

Another thing is that I the domain name comes up with a 403 error cannot view because of access permissions?

Any help please.