exchange 2003

I have successfully installed SERVER 2003, correctly configured DNS and completely create user in ACTIVE DIRECTORY. I also correctly installed EXCHANGE SERVER 2003, and the user has already created a mailbox. I succesfully log in the account created in Active Directory. That is the thing that I only did. The problem is, as a client when I open my OUTLOOK, it cannot continue, the message error appear “The Microsoft Exchange Server is unavailable. Outlook must be online or connected to complete this action”. I cannot use my e-mail because outlook cannot be establish. What should I do? Is there’s something or missing on my configuration? Please help me step by step so that I can use e-mail. Your help will be higly appreciated. Thank you