In a recent post, I wanted to upload a Stuffit file with a .sitx extension, but had a problem using the upload features in WordPress (error was “file type does not meet security guidelines”). After some searching, I found this article describing how to fix this problem (modifying wp-includes/functions.php to add ‘sitx’ => ‘application/x-stuffit’). Once I updated the file, I was able to upload the Stuffit file successfully.