From my perspective having a message have a valid signature with one
implementation and having a broken signature with another is an
incompatibility. I don't think that's speculation. ...
No, it merely reflects a difference of opinion by the sites concerned as
to what changes it will tolerate in a message before it recommends to its
clients that the message should be dropped. It is not the job of our
standard to dictate local policy issues at that level of detail.
I agree that we are not dictating local policy. But I really think that
it's our job to dictate the definition of what the signature validation
algorithm is. As I've said before, everyone remains free to do whatever
they want with messages whether or not the signature verifies, including
applying various heuristics to develop opinions about unsigned messages.
NOTE WELL: This list operates according to