Mitch Rerek wrote, in part:
> I wanted to make sure that the 'from' field was null so that
 > the recipients wouldn't be able to see the sender's address
 > and respond to them.

If this is an announcement list where one or a very few post, then
simply dream up an appropriate (valid, at least in syntax) "From:"
address, use it, and configure the list to accept the address or accept
the address for review.  For example, if one of my list owners wanted to
do this, I might suggest they send their posts "From:" the address
"[log in to unmask]".  That address happens to be a black hole, but the
address you choose could be undefined, I suppose.  But then I'm of the
opinion that if one can't reply to a piece of e-mail, it shouldn't have
been sent in the first place. Just MHO. :-)

If this is a discussion list, perhaps e-mail is not the appropriate vehicle?