Send email to an SMTP endpoint using STARTTLS. (from AWS Developer Guide)

gistfile1.cs

public static void SendWithSMTP(string username, string password, string host, int port)
{
    using (var client = new System.Net.Mail.SmtpClient(host, port))
    {
        client.Credentials = new System.Net.NetworkCredential(username, password);
        client.EnableSsl = true;
        client.Send("from@example.com", "to@example.com", "This is a test subject.", "This is a test email message body.");
    }
}