INBOX=/home/kasperle/Maildir/.mailboxes.$EXT2
TARGET=$INBOX

...

if (    /^List-Id:[:space:]*<?![^ \t<>\.]*!(\.[A-Za-z0-9\.\-]*)?>?[:space:]*$/ || \
        /^(X-Mailing-List|List-Post):[:space:]*<(mailto:)?![^<:@]*!@[^>\.@]*!(\.[^>]*)?>[:space:]*$/ || \
        /^Received:.*(LISTSERV-.*).*[:space:]![^ @]*@[^\.@;]*!(\.[^;]*)?;/ || \
        /^Mailing-List: *list *![^ @]*@[^\.@;]*!(\.[^;]*)?;/ )
        {
                TARGET="$INBOX.lists.$MATCH2/"
        }

to $TARGET