May be it is your network connection..try with this code and do it again.i did this my self and it worked properly..
public void mail(string receiver,string msg,string subject,string attachment1,string attachment2)
{
try
{
System.Net.Mail.MailMessage MyMailMessage = new System.Net.Mail.MailMessage("cecblaboratory@gmail.com", receiver, subject, msg + " < CECB Experiments Results Updates >");
MyMailMessage.IsBodyHtml = false;
System.Net.NetworkCredential mailAuthentication = new System.Net.NetworkCredential("xxxxx@gmail.com", "password");
System.Net.Mail.SmtpClient mailClient = new System.Net.Mail.SmtpClient("smtp.gmail.com", 587);
string file = attachment1;
string file2 = attachment2;
Attachment attach = new Attachment(file);
Attachment attach2 = new Attachment(file2);
MyMailMessage.Attachments.Add(attach);
MyMailMessage.Attachments.Add(attach2);
mailClient.EnableSsl = true;
mailClient.UseDefaultCredentials = false;
mailClient.Credentials = mailAuthentication;
mailClient.Send(MyMailMessage);
MessageBox.Show("Mail sent success!");
}
catch (Exception )
{
MessageBox.Show("Check your Network Connection", "Invalid or Empty", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
mail(txtreceiver.Text,txtmessage.Text,txtMailSubject.Text,lblAttach2.Text,lblAttach1.Text);
hope this will work..