Sorting existing pine folders into other folders

I'm sure this is pretty rudimentry to those that know, but what command 
do I envoke to have procmail sort an existing Pine folder into other 
folders.  Specifically, I'd like to sort my sent-mail by who I sent it to.

TIA!
   
Aaron Turner -aka: aturner(_at_)netcom(_dot_)com > 
Junior(_at_)Cal(_dot_)State(_dot_)University(_dot_)Hayward
--Hanlon's Razor:  Never attribute to < aka: Falcon3PLT(_at_)aol(_dot_)com
    malice that which is adequately   > aka: 
75774,1000(_at_)compuserve(_dot_)com
        explained by stupidity.       < Finger for more info and PGP key.