How to fix error while sending email from windows from?

Question

System.Net.Mail.SmtpException: Failure sending mail. ---> System.IO.IOException: Unable to read data from the transport connection: net_io_connectionclosed.

at System.Net.Mail.SmtpReplyReaderFactory.ProcessRead(Byte[] buffer, Int32 offset, Int32 read, Boolean readLine)

at System.Net.Mail.SmtpReplyReaderFactory.ReadLines(SmtpReplyReader caller, Boolean oneLine)

at System.Net.Mail.SmtpReplyReaderFactory.ReadLine(SmtpReplyReader caller)

at System.Net.Mail.SmtpConnection.GetConnection(ServicePoint servicePoint)

at System.Net.Mail.SmtpTransport.GetConnection(ServicePoint servicePoint)

at System.Net.Mail.SmtpClient.GetConnection()

at System.Net.Mail.SmtpClient.Send(MailMessage message)

--- End of inner exception stack trace ---

at System.Net.Mail.SmtpClient.Send(MailMessage message)