Attached is a patch that uses the user-mail-address (as set from
posting-styles) as an argument to senmdail -f.  This ensures that the
envelope matches the From: which is preferable in all cases for me.

Mail list managers, funky mail programs (like outlook), and mail
gateways (notes<-->smtp) seem to place more trust in the envelope than 
the From: header.

Lars, I noticed that message-generate-new-buffer-clone-locals takes an 
optional second argument according to the documentation.  However, the 
actual code doesn't work that way -- the actual argument is ignored.
This isn't used much so it probably isn't a big deal, but maybe the
arg list should be modified to reflect the real behavior.