Alas, it looks like people are aren't following the rules laid down in
the RFC, which makes makes this mechanism an accident waiting to happen,
just like the ad-hoc things that preceeded it.
sounds like a good reason to declare the whole thing Experimental, or maybe
Historic...
Speaking as a co-chair of the RECEIPT WG, I'm not ready to do that just yet.
But I think it is important that implementors understand that the IETF is
serious about interoperability in general and this issue in particular, and
that if enough widely used implementations fail to conform to the standard they
are likely to lose their shot at having a standardized mechanism.
It's not like the participants in this effort weren't warned...
Ned