In the Reporting Services books online, under "Configuring a Report Server for E-Mail Delivery", and under "RSReportServer Configuration File Settings", it states:

"The following settings are in the rsreportserver.config configuration file. " 

The first setting in the table is for "SMTP server" and its description is: 

"Specifies a string value indicating the address of the mail server. An alternative way to specify the SMTP server is through an IP address."

I also checked my installation of reporting Services and found my Email server listed in the rsreportserver.config file, not in the rswebapplication.config file.

The entry in rsreportserver.config looks like this:

Type="Microsoft.ReportingServices.EmailDeliveryProvider.EmailProvider,ReportingServicesEmailDeliveryProvider">

    <MaxRetries>3</MaxRetries>

    <SecondsBeforeRetry>900</SecondsBeforeRetry>

    <Configuration>

     <RSEmailDPConfiguration>

      <SMTPServer>exchsrv1</SMTPServer>

Am I missing something here or are none of the answers correct?