From: sender@example.invalid
Content-Type: multipart/mixed; boundary="BOUNDARY"
Mime-Version: 1.0
Subject: Inline image sandwiched between two text parts
Message-Id: <text-sandwiched-inline-image@example.invalid>
Date: Thu, 12 Nov 2020 09:41:00 -0800
To: recipient@example.invalid

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Here's that pic of that beautiful landscape.

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iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAAAAAA6fptVAAAACklEQVR4nGMAAQAABQABDQottAAAAABJRU5ErkJggg==

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Don't leave me behind, I also wanna go.

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