以下に解説があるような、ないような・・・
http://mehdi.me/generating-html-emails-with-razorengine-basics-generating-your-first-email/

以下のサンプルAPPを参考に
https://github.com/mehdime/RazorEngineEmails

RazorEngineのバージョンは3.4でした。
V3.5は
TemplateService→RazorEngineServiceへと推奨が変わっており、
RazorEngineServiceを使うほうがどうやらいいみたい。


public static void StronglyTypedModel_RazorEngineService(string welcomeEmailTemplatePath)
{
    var config = new TemplateServiceConfiguration();
    config.Language = Language.CSharp; // VB.NET as template language.
    //config.EncodedStringFactory = new RawStringFactory(); // Raw string encoding.
    config.EncodedStringFactory = new HtmlEncodedStringFactory(); // Html encoding.\


    var service = RazorEngineService.Create(config);
    Engine.Razor = service;


    // Generate the email body from our email template
    var stronglyTypedModel = new UserModel() { Name = "Sarah", Email = "sarah@mail.example", IsPremiumUser = false };


   // string template = "Hello @Model.Name, welcome to RazorEngine!";
    string templateFile = welcomeEmailTemplatePath;
    var template = new LoadedTemplateSource(File.ReadAllText(templateFile), templateFile);
    var result = Engine.Razor.RunCompile(template, "templateKey", null, stronglyTypedModel);


    // Send the email
    var email = new MailMessage()
    {
        Body = result,
        IsBodyHtml = true,
        Subject = "Welcome (generated from strongly-typed model)"
    };

    email.To.Add(new MailAddress(stronglyTypedModel.Email, stronglyTypedModel.Name));

    var smtpClient = new SmtpClient();
    smtpClient.Send(email);

    service.Dispose();
}

送信元のアドレスやSMTPの定義はどこで？と思ったらApp.configで設定するみたいです。

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
    </startup>

    <system.net>
        <mailSettings>
            <!-- Use the optional 'from' attribute to specify a default sender name and email if none is set in code -->
            <smtp deliveryMethod="Network" from="John &lt;john@awesomesite.com&gt;">
                <network host="localhost" />
            </smtp>
        </mailSettings>
    </system.net>
</configuration>