What should you do?

You have a server named Server1 that runs Windows Server 2008 R2. The server has the Web Server (IIS) server role installed.
You have an SMTP gateway that connects to the Internet.
The internal firewall prevents all computers, except the SMTP gateway, from establishing connections over TCP port 25.
You configure the SMTP gateway to relay e-mail for Server1.
You need to configure a Web site on Server1 to send e-mail to Internet users.
What should you do?

A.
On Server1, install the SMTP Server feature.

B.
On Server1, configure the SMTP E-mail feature for the Web site.

C.
On an internal DNS server, create an MX record for Server1.

D.
On an internal DNS server, create an MX record for the SMTP gateway.

Explanation:
Configure SMTP E-mail (IIS 7)
Configure SMTP e-mail in IIS when you want to deliver e-mail messages from your site. Mail can be delivered immediately or it can be delivered to a file location on disk where it can be retrieved for delivery later. For example, a company can provide an e-mail link for sending feedback messages or for requesting information.
To configure SMTP e-mail for a Web application
1. Open IIS Manager and navigate to the level you want to manage. For information about opening IIS Manager, see Open IIS Manager (IIS 7). For information about navigating to locations in the UI, see Navigation in IIS Manager (IIS 7).
2. In Features View, double-click SMTP E-mail.
3. On the SMTP E-mail page, type the e-mail address of the sender in the E-mail address text box.
4. On the SMTP E-mail page, select one of the following delivery methods:
a. Deliver e-mail to SMTP server: to deliver e-mail messages immediately. This requires an operational SMTP server for which the user has credentials.
b. Store e-mail in pickup directory: to store e-mails in a file location on disk for later delivery by an application such as an ASP.NET application, or by a user, such as an administrator.
5. If Deliver e-mail to SMTP server is selected, do the following:
a. Type the unique name of your SMTP server in the SMTP Server text box or select the Use localhost box to set the name to LocalHost. Setting the name to LocalHost means that ASP.NET will use an SMTP server on the local computer. Typically, this is the default SMTP virtual server.
b. Enter a TCP port in the Port text box. Port 25 is the SMTP standard TCP port and is the default setting. More than one virtual server can use the same TCP port if all servers are configured by using different IP addresses.
c. Under Authentication Settings, specify the authentication mode and credentials if your SMTP server requires these.
6. If Store e-mail in pickup directory is selected, type the batch e-mail location in the Store e-mail in pickup directory text box.
7. Click Apply in the Actions pane.
Source: http://technet.microsoft.com/en-us/library/cc772058(WS.10).aspx