Sending email

Hi,

I'm trying to make a function work.

I made a web application that will send email to user. User email could be hotmail, gmail or any other email. When sending email to myself (winhost hosted account) it's working but when trying to send to other email, I get this MailBox unavailable error : "Mailbox unavailable. The server response was: Authentication is required for relay"

This is my function :

private void SendMail(string from, string to)
{
try
{
//create the mail message
MailMessage mail = new MailMessage();
//set the addresses
mail.From = new MailAddress("[email protected]");
mail.To.Add(to); // can be gmail, hotmail or any other email

//set the content
mail.BodyEncoding = Encoding.UTF8;
mail.Subject = "Bla bla bla";
mail.Body = "Bla Bla Bla";

//send the message
SmtpClient smtp = new SmtpClient("mail.MyWinHostDomaine.com");

NetworkCredential Credentials = new NetworkCredential("[email protected]", "MyPassword");
smtp.Credentials = Credentials;
smtp.Send(mail);
writeToLog("Email Sent !", 2);
}
catch (Exception e)
{
Console.WriteLine(e.Message);
writeToLog("Email error" + e.Message, 1);
}
}

Thanks for the help