PHP: comment obtenir L'URL de referrer?

j'ai une page (index seulement) où les clients peuvent m'envoyer des emails et je veux voir de quel site web le visiteur vient?

Comment puis-je obtenir Referrer URL avec PHP? J'ai essayé avec $_SERVER['HTTP_REFERER'] mais il est vide tout le temps. Comment puis-je faire cela? Je vous remercie!

voici ce que contient mon $_SERVER ("- - - censuré - - - - "est censuré par moi)

array(31) {
  ["DOCUMENT_ROOT"]=>
  string(33) "/home/anything/public_html/design"
  ["GATEWAY_INTERFACE"]=>
  string(7) "CGI/1.1"
  ["HTTP_ACCEPT"]=>
  string(129) "text/html, application/xml;q=0.9, application/xhtml+xml, image/png, image/webp, image/jpeg, image/gif, image/x-xbitmap, */*;q=0.1"
  ["HTTP_ACCEPT_ENCODING"]=>
  string(13) "gzip, deflate"
  ["HTTP_ACCEPT_LANGUAGE"]=>
  string(14) "en-US,en;q=0.9"
  ["HTTP_CACHE_CONTROL"]=>
  string(8) "no-cache"
  ["HTTP_CONNECTION"]=>
  string(10) "Keep-Alive"
  ["HTTP_COOKIE"]=>
  string(189) "__utma=76630272.1468291432.1367655794.1367669576.1367674157.3; __utmb=76630272.1.10.1367674157; __utmc=76630272; __utmz=76630272.1367655794.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none)"
  ["HTTP_HOST"]=>
  string(25) " ---- CENSORED ---- "
  ["HTTP_USER_AGENT"]=>
  string(57) "Opera/9.80 (Windows NT 6.1) Presto/2.12.388 Version/12.15"
  ["PATH"]=>
  string(13) "/bin:/usr/bin"
  ["QUERY_STRING"]=>
  string(0) ""
  ["REDIRECT_STATUS"]=>
  string(3) "200"
  ["REMOTE_ADDR"]=>
  string(10) "5.15.68.79"
  ["REMOTE_PORT"]=>
  string(5) "57897"
  ["REQUEST_METHOD"]=>
  string(3) "GET"
  ["REQUEST_URI"]=>
  string(12) "/referer.php"
  ["SCRIPT_FILENAME"]=>
  string(45) "/home/anything/public_html/design/referer.php"
  ["SCRIPT_NAME"]=>
  string(12) "/referer.php"
  ["SERVER_ADDR"]=>
  string(13) " ---- CENSORED ---- "
  ["SERVER_ADMIN"]=>
  string(35) " ---- CENSORED ---- "
  ["SERVER_NAME"]=>
  string(25) " ---- CENSORED ---- "
  ["SERVER_PORT"]=>
  string(2) "80"
  ["SERVER_PROTOCOL"]=>
  string(8) "HTTP/1.1"
  ["SERVER_SIGNATURE"]=>
  string(189) "
Apache/2.2.19 (Unix) mod_ssl/2.2.19 OpenSSL/0.9.8e-fips-rhel5 mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/5.0.2.2635 Server at ---- CENSORED ---- Port 80

"
  ["SERVER_SOFTWARE"]=>
  string(125) "Apache/2.2.19 (Unix) mod_ssl/2.2.19 OpenSSL/0.9.8e-fips-rhel5 mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/5.0.2.2635"
  ["UNIQUE_ID"]=>
  string(24) "UYUNcUPeiDsAABkR2eYAAAAj"
  ["PHP_SELF"]=>
  string(12) "/referer.php"
  ["REQUEST_TIME"]=>
  int(1367674225)
  ["argv"]=>
  array(0) {
  }
  ["argc"]=>
  int(0)
}