<p>Thanks! Indeed, this turns threading off in gmail, which I think is ok for the time being.</p>
<p>Assuming we change some of the wording of those messages, we could remove the <code>X-Entity-Ref-ID </code>header at a later point in time. In particular there's no need to include <code>%{user}</code> in the email subject, as we already have that very same information in the "From:" header (at least on production).</p>

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