Add MIME (upload .msg file)

I tried echoing with mime_content_type, and I got 'CDF V2 Document, corrupt: Cannot read summary info' again. It does work for other files though (tried it with 'index.php', and it works with that).

I already checked that link before I asked my question here, if I add those lines into my .htaccess file, then I still get the same message: 'CDF V2 Document, corrupt: Cannot read summary info'. But my guess is, that the link is a solution for .docx files. Not for .msg files.