1- Create EmailTemplates Folder
---------------
2- Create Html Page Template Inject Razor Replacement Variables :

Test Email From NADY

@Model.SiteUrl

---------------
3- Install RazorEngine Nuget Package:
From Nuget Consol : PM> Install-Package RazorEngine -Version 3.5.3
https://www.nuget.org/packages/RazorEngine/3.5.3
// You can also check "razormachine"-> Install-Package razormachine

More Info :
https://github.com/Antaris/RazorEngine
http://antaris.github.io/RazorEngine/
https://razorengine.codeplex.com/
----------------
4- Create your Model :
- Called "TestEmailTemplateViewModel" :

public class TestEmailTemplateViewModel
{
public string UserFullName { get; set; }
public string UserName { get; set; }
public string RegDate { get; set; }
public string SiteUrl { get; set; }
}
----------------
5- Create Your test Controller "TestEmailTemplateController":

public ActionResult TestEmailTemplate()
{
return View();
}

[HttpPost]
public ActionResult TestEmailTemplate(string fortest)
{
ParsingTemplate();
return View();
}

private void ParsingTemplate()
{
//OR System.Web.Hosting.HostingEnvironment.MapPath(@"~/EmailTemplates/EmailTemplateTest.html");
string templateFilePath = System.Web.HttpContext.Current.Server.MapPath("~/EmailTemplates/EmailTemplateTest.html");
var templateAsString = System.IO.File.ReadAllText(templateFilePath);

var myViewModel = new TestEmailTemplateViewModel
{
UserFullName = "Mohamed Nady",
UserName = "NADY",
SiteUrl = "http://www.mohnady.com",
RegDate = DateTime.Now.ToString()
};

var body = RazorEngine.Engine.Razor.RunCompile(templateAsString, "templateKey", typeof(TestEmailTemplateViewModel), myViewModel);
// You Can Now Test your Returned Html Message Body (Check Body Value)

SendEmail("[email protected]", "[email protected]", "testEmail", body);

//=====================================================
//var result = RazorEngine.Engine.Razor.RunCompile("templateKey", typeof(TestEmailTemplateViewModel), myViewModel);
//============= Simple Example ========================
// string templateString = "Hello @Model.Name, welcome to RazorEngine!";
// var result = RazorEngine.Engine.Razor.RunCompile(templateString, "templateKey", null, new { Name = "World" });
//------------------------------
//string templateString = "Hello @Model.Name, welcome to RazorEngine!";
//string templateFileLocation = "C:/mytemplate.cshtml";
//var result = RazorEngine.Engine.Razor.RunCompile(new LoadedTemplateSource(templateString, templateFileLocation), "templateKey", null, new { Name = "World" });
// More Info: https://github.com/Antaris/RazorEngine
// http://antaris.github.io/RazorEngine/
//======================================================
}

private void SendEmail(string from, string to, string subject, string body)
{
// Sending .net Email Code
}

-----------------------
6- OR you can just Use Normal .Net Way using 'MailDefinition'

///

/// Other .Net Way To Send Email Using HTML Template File
/// Using Magic Of 'MailDefinition'
///

private void OtherDotNetNormalWayToSendEmailTemplate()
{
//How To Use Html Template To Send Email
string htmlBodyTemplatePath = System.Web.HttpContext.Current.Server.MapPath("~/EmailTemplates/EmailTemplateTest.html");
MailDefinition mailDefinition = new MailDefinition();
mailDefinition.BodyFileName = Server.MapPath(htmlBodyTemplatePath);
mailDefinition.From = "xxx";
mailDefinition.CC = "xxx";
mailDefinition.IsBodyHtml = true;
mailDefinition.Subject = "xxxx";
//------------
System.Collections.Specialized.ListDictionary replacements = new System.Collections.Specialized.ListDictionary();
replacements.Add("<%RegDate%>", "XXX");
replacements.Add("<%UserName%>", "XXXX");
replacements.Add("<%UserFullName%>", "XXX");
//------------
System.Net.Mail.MailMessage msg = mailDefinition.CreateMailMessage("XXX", replacements, new System.Web.UI.Control());
msg.From = new System.Net.Mail.MailAddress("XX", "XXX");
SmtpClient smtpClient = new SmtpClient();
smtpClient.Send(msg);

}