server 2003 exchange – smtp problem

hey,
i have ms server 2003 and exchange 2003 install.
i can recive mail/send mail in my domain, and also i can recive mail from outside.

my prblem is that i cannot send mail to outside domain.

this is the telnet outpot:
220 lbwserver.lbw.co.il Microsoft ESMTP MAIL Service, Version: 6.0.3790.3959 rea
dy at Sun, 27 Sep 2009 06:43:13 +0200
helo me
250 lbwserver.lbw.co.il Hello [192.168.1.100]
mail from:test@lbw.co.il
454 5.7.3 Client does not have permission to submit mail to this server.

Connection to host lost.

also i don’t understand i the user cannot send mail , how can he send to another user inside the lbw domain? becuase now they can send mail inside the domain.