Equations in email body render incorrectly

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

13.0

Where did you get the app from?

Google Play

Android version

16

Device model

Pixel 9

Steps to reproduce

Messages composed with TeX-style equations in Thunderbird Win11 128.2.0esr (Insert>Math) do not render correctly when displayed in K-9 MUA. Something close to the TeX markup appears instead of the equations.

These same messages are rendered correctly with Thunderbird, Roundcube, and Apple Mail (iPhone) MUAs.

Expected behavior

This is how the message is displayed in Thunderbird, Roundcube and Apple Mail

Actual behavior

This is how the message is displayed in K-9

Logs

The link explaining how to retrieve logs says only that its page is out of date.

Start by reproducing the issue in K-9 Mail 13.0 on Android with a message containing TeX-style equations composed in Thunderbird. Compare the displayed message with Thunderbird, Roundcube, and Apple Mail; done means the equations render correctly in K-9 Mail rather than exposing the markup. No source file or test is named, and the issue notes that the log-retrieval instructions are outdated.