e-mail sender address problem

[Donovan]

Hi

We have one Internet e-mail address. [email protected]
5 x Internal e-mail works fine internal [email protected].
We all can send email to the outside. (Internet)
Using sbs2k3 and outlook 2k3 on clients
Problem:
The e-mail we send to the outside show our local address as the sender can I
change this to show our Internet e-mail address [email protected] and not
[email protected]. - on all the clients?

Thanks in advance
Donovan