determining mime type

Hi All,

I have files in a directory that I need to display as a directory listing
onto a web page.  Users can click on the document and open the contents in
their browser.  I also have the files stored in an area not directly
accessible by the web server, for security purposes.  The script that
retrieves it gets the path and mime type from a mysql database before
opening and outputting the file's contents to the user's browser.  The mysql
database gets its information from another php script that is used to upload
and store the files.  When the files are stored, I can find out what mime
type it is and store it in the database.

Now, the users have a need to batch process a bunch of files (~50 files).
I've recommended that these batches of files be copied to the webserver by
ftp or some other means, and the users are fine with that.  However, the
problem arises: how does the script used to open the files and sends the
contents to the user's browser know what mime type it's sending?  What
happens if I don't specify any mime type in the header?  Will it be
displayed in the user's browser as if I had anyway?

-- 
Dang Nguyen