sorting mail by subject

> First, an apology for asking what looms to be an incredibly simple
> question (though I have read the man pages, various mini FAQs, tried
> searching the procmail archives and been reading this list for a couple 
> of months).
>
> I would like to sort mail from the procmail list (*not* sent in digest 
> form) by the subject header.  I'm using procmail v3.10 and csh.
 I cannot think of a procmail solution now, but mutt can be configured
 for threading. See http://www.cs.hmc.edu/~me/mutt/index.html.