2. Use of DKIM and SPF is reasonably well understood and does not
cause interesting email operations problems. I'm starting to hear some
unfortunate stories about DKIM signature breakage in scenarios that I'd
have hope would not have it, but the breakage of the signature is not
breaking legitimate email scenarios.
That's incorrect. The obvious counterexample is MIME downgrading, which was a
core MIME capability from the start.
I'm not Dave, but I think he meant that the DKIM design didn't depend on
signatures surviving through list managers. The list signs the mail and
recipients can use that.
We considered other ways to canonicalize but decided there was no way to
catch every plausible mutation (consider a list that flattens HTML to
plain text and then adds a footer), so we kept it simple.
R's,
John