I recently came across <a href="https://stackoverflow.com/questions/7263923/how-to-force-file-download-with-php" rel="nofollow">How to force file download with PHP</a> which describes setting
Content-Transfer-Encoding. Is this header applicable when used with this application when used to download a file via HTTP (it appears to be email related)? If so, what should it be set as for MS Word and Excel files, ZIP files, PDFs, and Text?
It has been religiously included by carg-cult copy-paste programmers since it was <a href="http://web.archive.org/web/20040209023954/http://www.php.net/manual/en/function.readfile.php" rel="nofollow">mentioned in a comment to the
readfile() manpage on PHP.net</a>.
It indeed <a href="https://stackoverflow.com/questions/7285372/is-content-transfer-encoding-an-http-header" rel="nofollow">has little to do with HTTP</a> and you can safely remove it.