The difference is that the Subject:, To: and l= advice don't dabble in the
area of having to tell a DKIM implementer to enforce parts of other protocols.
Adding a second From: makes the message format illegal. The other ones don't.
We're still talking past each other. You're right, it makes the message
format illegal, but so what?
Historically, there has been no reason for MUAs to enforce format
compliance on incoming messages. I get the impression that people expect
that to change. But why would it? "To catch stuff that DKIM chose not
to" isn't very compelling.
R's,
John
_______________________________________________
NOTE WELL: This list operates according to
http://mipassoc.org/dkim/ietf-list-rules.html