replacing urlencode with rawurlencode. It is possible that I've missed space

encoding as plus issue when I've tested IE or older php versions does not have
such behaviour. Should fix bug #1076733.

functions/mime.php

@@ -2017,7 +2017,7 @@ function magicHTML($body, $id, $message, $mailbox = 'INBOX') {
      // version
      //set all the Cache Control Headers for IE
      if ($isIE) {
-         $filename=urlencode($filename);
+         $filename=rawurlencode($filename);
          header ("Pragma: public");
          header ("Cache-Control: no-store, max-age=0, no-cache, must-revalidate"); # HTTP/1.1
          header ("Cache-Control: post-check=0, pre-check=0", false);