Re: authenticating the source of mail

>  Any comments on this approach?
yes.

1. it's a non-starter to force senders to submit to/relay through any 
   particular host or hosts.  people can and do send mail from anywhere, 
   and this is essential functionality.

2. my guess is that IESG isn't likely to approve a new use of, or 
   extensions to, the MS record.  

Keith