You also should figure out (most likely from your network administrator/IT department) if the SMTP server requires authentication. If so, you'll need to use a 3rd-party mailing class as PHP's mail() function doesn't support this feature.
EDIT: Note that using an Exchange server is certainly possible (I use our Exchange server at work to send mail via PHP myself), though there may be some slight configuration changes that need to be made so that Exchange will allow your webserver to send e-mails.