sending mail from localhost

I usually use a phpmailer class but am creating something from scratch. when I use the most basic example I can find: $to = 'nobody@example.com'; $subject = 'the subject'; $message = 'hello'; $headers = 'From: webmaster@example.com' . "\r\n" . 'Reply-To: webmaster@example.com' . "\r\n" . 'X-Mailer: PHP/' . phpversion(); mail($to, $subject, $message, $headers); I get this error <mail.blue-fly.co.uk>: sender address must contain a domain I am trying to send via my mail so have changed the lines in .ini to [mail function] ; For Win32 only. SMTP = mail.blue-fly.co.uk smtp_port = 25 ; For Win32 only. sendmail_from = mail.blue-fly.co.uk Thanks.