using Revalee.client to send email at background - asp.net-mvc-4

Question

Where should I call the revalee method to send mail email at background? What I am trying to achieve is to send email to the client if the expiration date is coming. I have follow the link: http://www.codeproject.com/Articles/738753/Scheduling-tasks-with-Revalee-and-MVC
My actionmethod is as follows:
public ActionResult SendExpirationMessage(int VehicleID)
{
// Validate the incoming request to ensure that this web app requested this callback
if (!RevaleeRegistrar.ValidateCallback(this.Request))
{
// Return a '401 Unauthorized' response to the Revalee service if the callback doesn't validate
return new HttpStatusCodeResult(HttpStatusCode.Unauthorized);
}
ApplicationDbContext db = new ApplicationDbContext();
var user = db.UserVehicleViewModels.Find(VehicleID);
var span = user.TaxDate.AddYears(1).Subtract(DateTime.Now);
int days = span.Days;
if (days >= 7)
{
System.Net.Mail.MailMessage m = new System.Net.Mail.MailMessage(
new System.Net.Mail.MailAddress("abc#abc.com", "Web Registration"),
new System.Net.Mail.MailAddress(user.Email));
m.Subject = "Tax Notification";
m.Body = string.Format("Dear {0} <BR/>This is an email to notify you about the due tax date of your vehicle, please pay tax on time. Thank you\" title=\"User Email Confirm\"></a>",
user.UserName);
m.IsBodyHtml = true;
System.Net.Mail.SmtpClient smtp = new System.Net.Mail.SmtpClient("smtp.gmail.com");
smtp.Credentials = new System.Net.NetworkCredential("abc#abc.com", "password");
smtp.EnableSsl = true;
smtp.Send(m);
}
the helper method is:
private void ScheduleExpirationMessage(int VehicleID)
{
// The server address where the Revalee service is installed
string revaleeServiceHost = "192.168.1.4";
// The callback will occur 27 days from now
DateTimeOffset callbackTime = DateTimeOffset.Now.AddMinutes(1.0);
// The url that will be called back, including userId
Uri callbackUrl = new Uri(
string.Format("http://localhost/UserVehicle/SendExpirationMessage/{0}", VehicleID));
// Register the callback request with the Revalee service
RevaleeRegistrar.ScheduleCallback(revaleeServiceHost, callbackTime, callbackUrl);
}