Error when sending via SMTP?

Exception: MailClient.Accounts.SocketException: Sending messages failed due to the following reason:
13:14:10.138|071| “Unable to read data from the transport connection: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond…”
13:14:10.138|071| at MailClient.Protocols.Smtp.SmtpSendCommand.Execute(WorkerStatus status)
13:14:10.138|071| at MailClient.Commands.Command.Process(WorkerStatus status)
13:14:10.139|030| AccountBase.ChangeOnlineState : State changed to OFFLINE due BrokenConnection