<p>As an example, GitHub uses an <code>In-Reply-To: <openstreetmap/openstreetmap-website/pull/2229@github.com></code> style header for replies. IIRC, this also works when you hit the "Subscribe" button where you never received the original message for an issue/pull request.</p>
<p>We could use a similar fake header, like <code>In-Reply-To: <openstreetmap-diary-123456@openstreetmap.org></code>. We know that the message should be created for a diary comment, and each diary has a unique numeric identifier.</p>

<p style="font-size:small;-webkit-text-size-adjust:none;color:#666;">—<br />You are receiving this because you are subscribed to this thread.<br />Reply to this email directly, <a href="https://github.com/openstreetmap/openstreetmap-website/issues/2430?email_source=notifications&email_token=AAK2OLJOQQD4O65Z4OXT6FLQTFJEXA5CNFSM4JLUCXZ2YY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOEDWX52I#issuecomment-552435433">view it on GitHub</a>, or <a href="https://github.com/notifications/unsubscribe-auth/AAK2OLPDGIOX2B2TSVGJYKLQTFJEXANCNFSM4JLUCXZQ">unsubscribe</a>.<img src="https://github.com/notifications/beacon/AAK2OLISB7AYZ3AQ77Z265LQTFJEXA5CNFSM4JLUCXZ2YY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOEDWX52I.gif" height="1" width="1" alt="" /></p>
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