Question

I want to do something, like edit my email address in a profile page, then return to the homepage saying it was successful – just like stackoverflow does when you receive answers or earn a new badge.

Answer 1

Try using TempData:

public ActionResult PostUserEmail(string email)
{
    TempData["Message"] = 'Email address changes successfully';
    return RedirectToAction("HomePage");
}

public ActionResult HomePage(string email)
{
    ViewData["Message"] = TempData["Message"];
    return View();//Use ViewData["Message"] in View
}

TempData["Message"] will be still there after redirection. TempData persists to next request, then it is gone.