Cannot sent email from windows form application

I get the following error message from the code below (note: av is turned off) where "HostedDomain" is my dasp domain - thanks in advance for any help.

Message "Failure sending mail."
InnerException {"Unable to connect to the remote server"} System.Exception {System.Net.WebException}


MailMessage message = new MailMessage();
MailAddress fromAddress = new MailAddress("[email protected]", "user name");

message.From = fromAddress;
message.To.Add("[email protected]");
message.Subject = "subject";
message.IsBodyHtml = false;
message.Attachments.Add(new System.Net.Mail.Attachment(filename));

SmtpClient mailClient = new SmtpClient();
NetworkCredential credential = new NetworkCredential("[email protected]", "password");

mailClient.Host = "smtp.HostedDomain.com";
mailClient.UseDefaultCredentials = false;
mailClient.Credentials = credential;

mailClient.Send(message);

 

...Have you tried "localhost" as the host?