The interesting thing in an organization is to have secure access from the outside, That's what DMZs are used for, and logically we're not going to put an Exchange server in it with its mailboxes, since users do not need to access from the LAN to the DMZ. What you do is create one or more servers that act as a Front-End in the DMZ that have Exchange, but only for external connections, SMTP and HTTP/HTTPS traffic would enter so that users from the internet can view mail by OWA. In this step, we will create a Front-End server and see how it would be configured. It is assumed that in the LAN we will already have our(s) server(is) with MS Exchange mailboxes accessed from the LAN with MS Outlook-type mail clients.