Re: The spam problem.

[David S. Miller]

Nobody has mentioned the fact that spammers can forge the
From: field just like anyone else can.

If you enforce that the first sender at the Received: headers
have to match the From: or some rule like that, then I could
not post to these lists for example.

This is why enforcing that subscribers only can post to the lists is
totally unacceptablt.  It doesn't stop spam, it's merely a deterrant
and it serves mostly to piss off legitimate users of these lists.