None of this seems to work. 

They are both using System.Web.Mail

I need to know how to use the new System.Net.Mail

Here is my controller if this my help:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using SteamKing.Models;
using System.Net.Mail;


namespace SteamKing.Controllers
{
    public class Contact_UsController : Controller
    {
        //
        // GET: /Contact_Us/
         [HttpGet]
        public ViewResult Index()
        {
             
            return View();
        }
         [HttpPost]
         public ViewResult Index(Contact_Us Index)
         {
             if (ModelState.IsValid)
             {
                 //I need the Email sender to go here.
                 return View("Thanks", Index);
             }
             else
             {
                 return View();
             }
         }
    }
}

Also here is my View:

@model SteamKing.Models.Contact_Us

@{
    ViewBag.Title = "Contact_Us";
}

<h2>Contact_Us</h2>
<fieldset>
<legend>Send Steam King a Message!</legend>
 @using (Html.BeginForm())
 { 
    @Html.ValidationSummary()
    <p>First Name:</p>
    <p>@Html.TextBoxFor(m => m.firstName)</p>
    <p>Last Name:</p>
    <p>@Html.TextBoxFor(m => m.lastName)</p>
    <p>Phone Number:</p>
    <p>@Html.TextBoxFor(m => m.phoneNumber)</p>
    <p>Email:</p>
    <p>@Html.TextBoxFor(m => m.email)</p>
    <p>Are you a previous customer:</p>
    @Html.DropDownListFor(x => x.previousCustomer, new[] {
                    new SelectListItem() {Text = "Yes, I am", Value = bool.TrueString},
                    new SelectListItem() {Text = "No, I am not", Value = bool.FalseString}
                }, "Choose an option")
    <p>Message:</p>
    <p>@Html.TextAreaFor(m => m.message, new { @cols = 80, @rows = 10 })</p>
    <input type ="submit" value="Submit" />
 }
</fieldset>

so i need to be able to send that form to the Clients email address letting them know who sent it and what was said in the message