Subject: Test message with attached message
From: [email-masked]
To: [email-masked]
Date: Sat, 30 Dec 2017 19:12:38 +0100

This is a test message with an attached message.

Subject: Attached message (plaintext + HMTL, both base64 encoded)
From: [email-masked]
To: [email-masked]
Date: Sat, 30 Dec 2017 19:31:21 +0100

Here is the body of the attached message. Search for bodyOfAttachedMessagePlain.