SMTP Not sending out the mail fro the queue

Dear all,

We have a W3K3server with SMTP enabled a firewall box protecting the server.
There are two network cards in the server where one is used by the data
centre for backup purposes which is using a dynamic ip and the other
configured to connect to the other servers using a ip range 128.0.0.x.

There is an external ip mapped to the DNS. this is mapped using NAT to the
internal ip 128.0.0.3.

The firewall is expecting transactions for configured services (SMTP/HTTP)
from computers in the 128 range.

my problem is whenever i queue a mail, it goes to ..\inetpub\mailroot\queue
and does not go out from there!

Can someone please help me troubleshoot this?
Many Thanks

Kind Regards,
Devapriya De Silva