+1. Issues come when senders try to keep the same fromHeader or DKIM
authentication while making changes or acting as a malicious forwarder.
Since you’re not doing either of those and changing the domain in the DKIM
authentication to take ownership of the message I don’t think there is
anything unusual to be concerned of.

Best,
Emanuel

On Tue, Jun 16, 2026 at 10:33 AM Bron Gondwana <brong=
[email protected]> wrote:

> On Mon, Jun 15, 2026, at 16:37, william.weiner=
> [email protected] wrote:
>
> Bron,
>
> Thanks for confirming the originator framing.
>
> On the nonce: the SES message ID is a natural fit. It is already opaque to
> outsiders, it is the S3 object key, and it is a direct lookup into storage
> we already have -- no extra bookkeeping. One thing worth noting: a nonce
> past the 30-day retention window is a transparency statement, not a gap.
> The S3 object is gone by design at that point. That is a privacy feature.
>
> On Message-ID: yes, we do rewrite it. We also scrub References and
> In-Reply-To, rewriting them to our own domain namespace. Thread identifiers
> in the originating provider's format would otherwise propagate sender and
> provider information across the relay boundary.
>
> On the considerations text: intentional re-origination by a
> privacy-preserving intermediary should be acknowledged as a legitimate
> deployment pattern, so that an assumed missing chain is not read as evasion
> by downstream deployment or reputation guidance. There are many people who
> want this level of privacy in their email. Recipient privacy is a
> first-class use case. Happy to propose text if that would help move it
> forward.
>
>
> I really don't think there's any text required at all, but if there was it
> would belong in draft-herr-dkim2-bcp.
>
> You're basically creating a brand new message out of some cherry-picked
> parts of a message which came into your system.  It's not "the same email"
> in any meaningful sense, and you're deliberately NOT providing a chain of
> custody through your systems - the opposite of what DKIM2 (or indeed ARC,
> or even just the Received headers) is designed to do.
>
> So you're doing something completely different to DKIM2; up until you send
> the message out into the rest of the world again, in which case it's a new
> message and you quite rightly take ownership of it.
>
> Bron.
>
> --
>   Bron Gondwana, CEO, Fastmail Pty Ltd / Fastmail US LLC
>   [email protected]
>
>
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