Envoyer un mail avec visual studio et Gembox

private async void UnlockDoor(string visitorName)
        {
            // Greet visitor
            await speech.Read(SpeechContants.GeneralGreetigMessage(visitorName));
            string DateHeure = DateTime.Now.ToString();
 
            // If using Professional version, put your serial key below.
            ComponentInfo.SetLicense("FREE-LIMITED-KEY");
 
            // Create new message
            MailMessage message = new MailMessage(new MailAddress("xxxxxtor@gmail.com", "Sender"),
                                                  new MailAddress("xxxxxbizet2@gmail.com", "First receiver"));
 
            // Add second receiver to CC and set subject
            // message.Cc.Add(new MailAddress("second.receiver@example.com", "Second receiver"));
            message.Subject = "Historique ouverture porte";
 
            // Add attachment
            // message.Attachments.Add(new Attachment("C:\\GemBox\\Email\\CommonUses\\Picture.jpg"));
 
            // Add HTML and text body
            message.BodyText = visitorName + DateHeure;
 
            // Initialize new SMTP client and send message
            using (SmtpClient smtp = new SmtpClient("<ADDRESS> (e.g. smtp.gmail.com)"))
            {
                smtp.Connect();
 
                smtp.Authenticate("xxxxxxr@gmail.com", "xxxxx");
 
                smtp.SendMessage(message);
            }
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