1.
            private void button1_Click(object sender, EventArgs e) {
   2.
                 DialogResult dr = MessageBox.Show("Send email?", "Get Permission", MessageBoxButtons.YesNo, MessageBoxIcon.Question,
   3.
                     MessageBoxDefaultButton.Button2);
   4.
       
   5.
                 if (dr == DialogResult.Yes) {
   6.
       
   7.
                     SmtpClient smtpClnt = new SmtpClient("smtp.gmail.com", 587);
   8.
       
   9.
                     try {
  10.
       
  11.
                         MailMessage oMail = new MailMessage();
  12.
                         oMail.To.Add(new MailAddress("[email protected]"));
  13.
                         oMail.From = new MailAddress("[email protected]");
  14.
                         oMail.IsBodyHtml = true;
  15.
       
  16.
                         oMail.Body = "your message body goes here";
  17.
                         oMail.Subject = "your subject goes here";
  18.
       
  19.
                         smtpClnt.Timeout = 100000;
  20.
       
  21.
                         smtpClnt.EnableSsl = true;
  22.
                         System.Net.NetworkCredential nc = new System.Net.NetworkCredential("[email protected]", "your_password");
  23.
                         smtpClnt.Credentials = nc;
  24.
       
  25.
                         Attachment oAttached = new Attachment("C:\\yourimage.jpg");
  26.
                         oMail.Attachments.Add(oAttached);
  27.
       
  28.
                         smtpClnt.SendCompleted += new SendCompletedEventHandler(MailDeliveryComplete);
  29.
       
  30.
                         smtpClnt.SendAsync(oMail, "sending");
  31.
       
  32.
                     }
  33.
                     catch (Exception mailExc) {
  34.
                         if (mailExc.ToString().IndexOf("could not be resolved") >= 0) {
  35.
                             int line = mailExc.ToString().IndexOf("line");
  36.
                             int leng = mailExc.ToString().Length;
  37.
                             string sLin = mailExc.ToString().Substring(line, (leng - line));
  38.
                             string s = "Either the developer's Gmail SMTP was unavailable, or else your computer is not currently ";
  39.
                             s += "connected to the internet.  Error generated at source code " + sLin;
  40.
                             MessageBox.Show(s, "Unable to send character file via email");
  41.
                         }
  42.
                         else {
  43.
                             MessageBox.Show("Error:" + Environment.NewLine + Environment.NewLine +
  44.
                                 mailExc.Message + Environment.NewLine + Environment.NewLine + mailExc.ToString());
  45.
                         }
  46.
                     }
  47.
                     finally {
  48.
       
  49.
                         //don't invoke smtpClnt.Dispose() here; if you do, the mail never sends
  50.
                     }          
  51.
       
  52.
       
  53.
                 }
  54.
             }
  55.
       
  56.
       
  57.
       
  58.
             private void MailDeliveryComplete(object sender, System.ComponentModel.AsyncCompletedEventArgs e) {
  59.
       
  60.
                 string myMessage = e.ToString();
  61.
                 string myCaption = string.Empty;
  62.
       
  63.
                 if (e.Error != null) {
  64.
                     myCaption = "Error sending email";
  65.
                 }
  66.
                 else if (e.Cancelled) {
  67.
                     myCaption = "Sending of email cancelled.";
  68.
                 }
  69.
                 else {
  70.
                     myCaption = "Your email message was sent successfully to the Game Master.";
  71.
                 }
  72.
       
  73.
                 MessageBox.Show(myMessage, myCaption);
  74.
       
  75.
             }

Notes:\r\n\r\n(1) your namespace\'s using section should include the following:\r\nusing System.Net.Mail;\r\n\r\n(2) my example code places the email-sending code in a Button\'s Click() event-handler

Send Gmail email using C#

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C#