Cannot send email internally

Hi

We have just put Microsoft BackOffice Server on one of our
servers,in
order to use the Exchange feature,the reason for this is
that we just
had a diginet line installed,and you can only send mail
using one
ip,so we have to use exchange to enable every to send
mail,the problem
is that we cannot send mail to anybody in the company(in
our
domain),we can send mail to any anyother email addresses
except
ours,there are no errors on Outlook,and the mail goes form
the outbox
to sent items,but no one recieves the mail
Is there some sort of setup that needs to be done in order
to send
mail in the same domain?

PS: we just use exchange to send mail,our mailboxes
resides with other
company,so we dont have an actual mail server as such

Please help
Be specific if can,first time usindg E2k,not very
technical!!

Is there a wat to make the internal emails to go in the
mail box but to another host!!!