public static void SendViaSendGrid(this MailMessage mailMessage, string sendGridUsername, string sendGridPassword, bool sendAsync)
        {
            SmtpClient        smtpClient  = new SmtpClient("smtp.sendgrid.net", Convert.ToInt32(587));
            NetworkCredential credentials = new NetworkCredential(sendGridUsername, sendGridPassword);

            smtpClient.Credentials = credentials;

            mailMessage.SendViaSmtp(smtpClient, sendAsync);
        }