Cannot get content-type: text/plain

I am trying to get Contact Form 7 to send plain text emails with appropriate line breaks. I have DE-selected the “use HTML content type” checkbox.

Upon doing that, the email arrives with no line breaks at all.

Message Body in CF7:

From: [first-name] [last-name]
Email: [email]
Phone: [phone]
Message Body: [message]

Message body received via email:

From: FIrstname Lastname Email: cvc1968@test.com Phone: 3045551212 Message Body: Test plain text email

I’ve tried various methods of inserting linebreaks that I have found online (ie. \r\n, \n, \r, \\n) and all just display whatever I’ve typed.

In CF7:

From: [first-name] [last-name] \r\n
Email: [email] \r\n
Phone: [phone] \r\n
Message Body: [message] \r\n

The received email:

From: FIrstname Lastname \r\n Email: cvc1968@test.com \r\n Phone: 3045551212 \r\n Message Body: Test plain text email line breaks using "rn" \r\n

So next I took a look at the raw source of the emails. In all cases, despite the fact that I have DE-selected “Use HTML content type” the headers all contain:
Content-Type: text/html; charset=UTF-8

So I tried adding the tex/plain header in the “Additional Headers Field” in CF7:

Reply-To: [email]
Content-Type: text/plain; charset=UTF-8

But it has no effect on the headers in the received message:

Content-Type: text/html; charset=UTF-8
From: XXXXX <do-not-reply@xxxxxx.org>
Sender: XXXXX <do-not-reply@xxxxxx.org>
To: carlvarney@xxxxxx.com
Reply-To: cvc1968@test.com
Subject: Message from xxxxxx Contact Form
Date: Mon, 15 Jun 2015 15:24:14 +0000
Content-Transfer-Encoding: quoted-printable
Content-Disposition: inline
MIME-Version: 1.0

What am I doing wrong and how can I get CF7 to send a plain text email with line breaks?

Thank you.

https://wordpress.org/plugins/contact-form-7/