I never realized this but you can set the default SMTP information in the .config file (Thanks Viktar!). This applies to the new System.Net.Mail.* classes (Not the deprecated System.Web.Mail.* classes). MSDN defines the elements here and here.

<configuration>
  <system.net>
    <mailSettings>
      <smtp deliveryMethod="network" 
         from="appointments@TrepanationNation.com">
        <network host="smtp.TrepanationNation.com" 
         port="25" defaultCredentials="true"/>
      </smtp>
    </mailSettings>
  </system.net>

The code is the same but you no longer have to specify the from and SMTP server details:

using (MailMessage message = new MailMessage())
{
    message.IsBodyHtml = true;
    message.To.Add("someguy@someserver.com");
    message.Subject = "Trepanation Appointment";
    message.Body = @"<b>This confirms your 
        Trepanation appointment this Friday.</b>";
    SmtpClient mailClient = new SmtpClient();
    mailClient.Send(message);
}