发送电子邮件时出现SmtpException

我正试图通过C#代码发送电子邮件，但我收到了SmtpException

连接尝试失败是因为连接方在一段时间后没有正确响应，或者建立的连接失败是因为所连接的主机没有响应173.194.67.109:587

以下是我发送电子邮件的方式：

string HostAddress = "smtp.gmail.com";
MailMessage msg = new MailMessage();
msg.From = new MailAddress(fromEmail);
msg.Subject = "Test Email";
msg.Body = "Hi testing invoice";
msg.IsBodyHtml = true;
msg.To.Add(new MailAddress("ramshaafaq2012@gmail.com"));
SmtpClient client = new SmtpClient();
client.Host = HostAddress;
client.EnableSsl = true;
NetworkCredential creadit = new NetworkCredential();
creadit.UserName = msg.From.Address;
creadit.Password = Password;
client.UseDefaultCredentials = true;
client.Credentials = creadit;
client.Port = 587;
client.Send(msg);

client.UseDefaultCredentials = true;
client.Credentials = creadit;