"Show headers" collapses multi-line headers onto one line, making them not authentic and often unreadable

Checklist

• I have used the search function to see if someone else has already submitted the same bug report.
• I will describe the problem with as much detail as possible.

App

K-9 Mail

App version

10.1

Where did you get the app from?

F-Droid

Android version

LineageOS 22.2

Device model

Xperia XZ2 compact

Steps to reproduce

1. Go to a received email
2. Make sure fully downloaded ("Download complete message" if necessary; to avoid bug #5240)
3. Press the three-dots button for the menu
4. "Show headers"

Expected behavior

I would expect to see an actual representation of the headers, verbatim as they are present in the source. Similar to "Show original" in desktop Thunderbird. Specifically with: newlines still in place; fixed-width font for alignment.

Because if I'm viewing the headers then I'm seeking accurate, unprocessed information.

For example:

X-Spam-Score: 10.1
X-Spam-Level: ++++++++++
X-Spam-Report: Spam detection software, running on "xxxxxxxxxx"
 
 Content analysis details:   (10.1 points, 4.0 required)
 
  pts rule name              description
 ---- ---------------------- --------------------------------------------------
  1.4 MISSING_DATE           Missing Date: header
  0.5 MISSING_MID            Missing Message-Id: header
  0.0 DKIM_ADSP_CUSTOM_MED   No valid author signature, adsp_override is
                             CUSTOM_MED
  0.8 BAYES_50               BODY: Bayes spam probability is 40 to 60%
                             [score: 0.5005]
  0.0 TVD_RCVD_IP            Message was received from an IP address
  0.0 FREEMAIL_FROM          Sender email is commonly abused enduser mail provider
                             [xxxxxxxxx(at)gmail.com]
  1.0 FORGED_GMAIL_RCVD      'From' gmail.com does not match 'Received' headers
  0.0 HTML_MESSAGE           BODY: HTML included in message
  0.1 MIME_HTML_ONLY         BODY: Message only has text/html MIME parts
  0.4 HTML_MIME_NO_HTML_TAG  HTML-only message, but there is no HTML tag
  1.0 RDNS_DYNAMIC           Delivered to internal network by host with
                             dynamic-looking rDNS
  0.4 KHOP_HELO_FCRDNS       Relay HELO differs from its IP's reverse DNS
  0.9 NML_ADSP_CUSTOM_MED    ADSP custom_med hit, and not from a mailing list
  0.4 RCVD_IN_XBL            RBL: Received via a relay in Spamhaus XBL
                             [34.141.xx.xx listed in zen.spamhaus.org]
  3.3 RCVD_IN_SBL_CSS        RBL: Received via a relay in Spamhaus SBL-CSS
                             [34.141.xx.xx listed in zen.spamhaus.org]
X-Spam-Flag: YES

Actual behavior

The headers get collapsed onto one line:

Logs

No response