I'm developing a simple send mail app in C#, using my CMail Server:

MailMessage mail = new MailMessage("[email protected]", "[email protected]");
        mail.Subject = "Sub";
        mail.Body = "Hi!";
        SmtpClient smtp = new SmtpClient("MyServer");
        System.Net.NetworkCredential cred = new System.Net.NetworkCredential("user", "pass");
        smtp.UseDefaultCredentials = false;
        smtp.Credentials = cred;
        smtp.Send(mail);

Obviously i ommited my account information, so, this code throws me an Authentication Exception for some reason. I first thought that the code was wrong, so i change the info to my gmail account and everything goes fine, with the only SMTP server that i having trouble is with the CMail. Is there a problem with .NET and CMail's SMTP ?

Thanks for the help and comments!