[exim] Help with using a numerical variable in a MIME ACL

I have tried the following in a MIME ACL but the $1 numerical variable
does contain anything:

# Discard e-mail with graphic file attachment.
        discard condition       =       ${if match
{${lc:$mime_filename}} {[.] *(gif|jpg|jpeg|png|bmp)\$}}
                !sender_domains =       +ok_domains
                logwrite        =       External e-mail from
'$sender_address' with invalid attached file type ($1) '$mime_filename'
- discard!

Searched the current on-line documentation and the Wiki but can't find
an example for what I am after.

Not sure if I want to do is possible.


Any help would be appreciated.



Thanks


Paul McIlfatrick