login SMTP send mail error : Unable to read data from the transport connection: net_io_connectionclosed

client.Credentials = new NetworkCredential(sSMTPuser, sSMTPpass);

client.Credentials = new NetworkCredential(user@domainName.com, sSMTPpass);

用户名需要带上域名，真是脑残的邮件服务器： 亿邮。