formail not working?

Ok, I am refining my original request. Right now I'm not even worried about
checking mlist.ppl for a valid sender. All I want to do now is: (in
pseudo-code)

if there is a header that matches "X-Rcpt-To: mlist(_at_)herp(_dot_)com" and
   there is not a header that matches "X-Loop: mlist(_at_)herp(_dot_)com" then
        Add a header that says "X-Loop: mlist(_at_)herp(_dot_)com" and
        Send the modified message to all email addresses listed in mlist.ppl
else
        continue through the rc file for further recipes
end if

Here are a few variations of the recipe that I've tried to accomplish this:

:0c
* ^X-Rcpt-To(_dot_)*mlist(_at_)herp(_dot_)com
* !^X-Loop: mlist(_at_)herp(_dot_)com
! formail -A "X-Loop: mlist(_at_)herp(_dot_)com"
! `cat mlist.ppl`

:0c
* ^X-Rcpt-To(_dot_)*mlist(_at_)herp(_dot_)com
* !^X-Loop: mlist(_at_)herp(_dot_)com
! formail -A "X-Loop: mlist(_at_)herp(_dot_)com" | `cat mlist.ppl`

:0c
* ^X-Rcpt-To(_dot_)*mlist(_at_)herp(_dot_)com
* !^X-Loop: mlist(_at_)herp(_dot_)com
! (formail -A "X-Loop: mlist(_at_)herp(_dot_)com") | `cat mlist.ppl`

:0c
* ^X-Rcpt-To(_dot_)*mlist(_at_)herp(_dot_)com
* !^X-Loop: mlist(_at_)herp(_dot_)com
! `cat mlist.ppl` | (formail -A "X-Loop: mlist(_at_)herp(_dot_)com")

If I remember correctly, they all resent the UNMODIFIED message
to all recipients in mlist.ppl. But, I was never able to add that X-Loop
header. Now that I've spammed myself so much, I really would like
some help.

Thank you,

Bryan Mohr