自动将电子邮件发送到不同的网域

我已经创建了注册页面，该页面将自动向用户发送电子邮件以确认他们的帐户。是否有任何方法可以将符合性的电子邮件发送到不同的域，如hotmail、yahoo、live等。。所有不同的域（包括.com、.uk、.org等）。如果可以的话，我可以获得关于如何在c#中使用代码/修改代码的代码/文章吗。。这是我发送电子邮件的代码。

 using (MailMessage mm = new MailMessage("sender@mydomain.com", txtEmail.Text))
    {
        mm.Subject = "Account Activation";
        string body = "Hello " + txtUsername.Text.Trim() + ",";
        body += "<br /><br />Please click the following link to activate your account";
        body += "<br /><a href = '" + Request.Url.AbsoluteUri.Replace("CS.aspx", "CS_Activation.aspx?ActivationCode=" + activationCode) + "'>Click here to activate your account.</a>";
        body += "<br /><br />Thanks";
        mm.Body = body;
        mm.IsBodyHtml = true;
        SmtpClient smtp = new SmtpClient();
        smtp.Host = "smtp.gmail.com";
        smtp.Port = 587;
        smtp.EnableSsl = true;
        smtp.UseDefaultCredentials = false;
        NetworkCredential NetworkCred = new NetworkCredential("sender@gmail.com", "password");
        smtp.DeliveryMethod = System.Net.Mail.SmtpDeliveryMethod.Network;
        smtp.Credentials = NetworkCred;
        smtp.Send(mm);
    }