current mail filename

[Chris Uzdavinis <chris@atdesk.com>]

I receive some emails using nnml that need an external program to
process, and would like to setup a key-binding that spawns a shell and
passes the current mail filename to that script.  The emails already
saved to disk by Gnus in a directory corresponding to the split, and
then using an incrementing number for the filename.  

The only part that I don't know how to do is how to query Gnus for the
full filename of the the current email being read.  What function do I
call to get this, or what variable would I check to access this data?

(I'm wanting to set the key binding to work in the summary buffer for
the mail under the cursor, or if the active frame is the body of the
email, I'd like it to use the filename of the mail currently being
displayed.

Thanks in advance.

-- 
Chris