From: "Example Vendor" <vendor@example.test>
To: analyst@example.test
Subject: Quarterly review
MIME-Version: 1.0
Content-Type: multipart/alternative; boundary="demo-boundary"
DKIM-Signature: v=1; a=rsa-sha256; d=example.test; s=demo; bh=AAAAAAAA; b=BBBBBBBB

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Content-Type: text/plain; charset=UTF-8

Plain summary.
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Content-Type: text/html; charset=UTF-8

<p>Visible <strong>HTML</strong> summary.</p><img src="https://example.invalid/tracker.png" alt="">
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