note 35927 added to function.mail

I am having a problem with the mail() function, "Warning: mail(): SMTP server response: 501 5.5.4 Invalid Address in d:\inetpub\wwwroot\hs\mathtesting\mathcenter\something.php on line 7" could someone enlighten me on what the problem is? This is my code: <?php $to="Put the emails here Justin"; $mailsub="Help Request"; $body= "Name: " . $name . "\nGrade: " . $grade . "\nEmail: " . $emailno . "@hkis.edu.hk" . "\nDate: " . $date . "\nFrees: " . $frees . "\nSubject: " . $subject; mail($to, $mailsub, $body); ?> ---- Manual Page -- http://www.php.net/manual/en/function.mail.php Edit Note -- http://master.php.net/manage/user-notes.php?action=edit+35927 Delete Note -- http://master.php.net/manage/user-notes.php?action=delete+35927&report=yes Reject Note -- http://master.php.net/manage/user-notes.php?action=reject+35927&report=yes