How to send an email (.NET)?

Quote:

System.Net.Mail.SmtpException: 'The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.0 Authentication Required. Learn more at'

MailMessage message = new MailMessage("****@gmail.com", bl.BLFindCustomerMailByName(DDLUser.SelectedValue));
message.Body = mail;
message.Subject = title;
message.IsBodyHtml = true;
NetworkCredential mailAuthentication = new NetworkCredential("****@gmail.com", "***");
SmtpClient mailClient = new SmtpClient("smtp.gmail.com", 587);
mailClient.EnableSsl = true;
mailClient.UseDefaultCredentials = false;
mailClient.Credentials = mailAuthentication;
mailClient.Send(message);