I like this idea. It should be specified as a new extension that gives clients a way to trust the DKIM2 headers they see.
Third-party clients that aren't coupled to the MTA or message store currently have no way to establish that trust. Without it, we'll end up in a similar place as BIMI (leaving aside that its main problem is that’s it’s a business model dressed as a standard), with trust depending on provider-specific arrangements instead of anything the protocol guarantees. Best, Mauro > On 6 Nov 2026, at 4:39 am, Bron Gondwana > <[email protected]> wrote: > > > I figured -- why not add to Fastmail (on an experimental branch, this isn't > shipped) some code to show what you can do with Message-Instance diffs. > > This is about 150 lines of backend code and 600 lines of frontend code in > total (including a diff library), and implemented like this, taking advantage > of the super powers of JMAP: > backend has a Message-Instance parser, if the frontend requests the > dkim2History parameter then it gets parsed Message-Instances is a neat JSON > format, from which it can calculate any header changes. > backend has a synthetic blobId format which is x-dkim2-{m}-{blobId}. > frontend requests Email/parse: id=x-dkim2-1-$blobId to get a parsed version > of the original message, which gives it the HTML formatted version without > having to have any DKIM2 undo code on the client, it's all on the server > (which already has a library for undoing changes). > frontend creates DOMs from the original and current message, calculates the > diff, and presents it graphically. > This was a remarkably simple process thanks to the way that JMAP lets you > compose operations. Yay JMAP. > > Here's the pictures. The box at the top is presented for any message with a > recipe which changes the message: > > <image.png> > And here's the same message with changes shown: > <image.png> > I should probably make the green be a little more distinct, but it's quite > readable. I could easily see a UI like this being popular with more > technical people. But mostly I expect the actual diffs to be looked at by > antispam tools and agents in the future. > > DKIM2 is arriving right at the time where more and more people are having > automated tools look at their messages as well, and the accountability > tracking is really useful for agents, because they notice different things > than humans, and they're more easily fooled by some things - so having a > strictly formal definition of alignment and of change recipes play to their > strengths. > > Bron. > > > -- > Bron Gondwana, CEO, Fastmail Pty Ltd / Fastmail US LLC > [email protected] > > _______________________________________________ > Ietf-dkim mailing list -- [email protected] > To unsubscribe send an email to [email protected]
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