windows server 2003 e-mail issues…not able to send/receive outside domain

Hello.

We are in desperate need of help. We are running a server with Windows Server 2003 on it. We are trying to setup the e-mail portion of the server and are having troubles. Our domain is tandmcomputers.ca. We are able to send to accounts within that domain BUT when I use another e-mail address (hotamil, ISP’s e-mail, etc) and try to send to “example@tandmcomputers.ca” we cannot receive it. We get a bouncback message from the e-mail provider we are sending from. Also we cannot send from “example@tandmcomputers.ca” to other e-mail address (hotmail, ISP’s e-mail, etc).

Any help or suggestions will be grately appreciated.