Reply to field

I'm trying to change the "reply to" field while keeping the "from" field 
in the header of a maling list intact, so everyon can see who sent 
the mail. I thought it would be easy. But for some reason it didn't 
work. I'v tried adding 

-I"Reply: diablo(_at_)mydom(_dot_)com"\
-I"Reply_to: diablo(_at_)mydom(_dot_)com"\

but niether worked.
Below  takes care of the reply part but of course at the expense of the 
from field. Also does anyone know where in the man page
is a list of all the fields, their respected names, and their exactly 
usage?

|(/opt/local/bin/formail -I"Organization: "\
-I"From: diablo(_at_)mydom(_dot_)com"\
...
...

Thanks
T. Bachis