No incoming mail body shown on many emails, just a link to file "email" to download

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

11.0

Where did you get the app from?

F-Droid

Android version

13

Device model

No response

Steps to reproduce

Open incoming mails, many have no message body at all, just file "email" to download a html file containing the message body and other attachments

Expected behavior

See message body, not just the file "email" with the html body to download

Actual behavior

Most mails show no email body, just the file "email" to download. Interestingly if you press the button "Reply", then the message body is shown in your reply, see attached screenshot (this is the same email from the screenshot above where only file "email" is seen for download). I have tried to find similar issues reported here but couldn't find any.

Logs

No response

No source file or test is named. Reproduce on Android 13 with K-9 Mail 11.0 using incoming messages that show only the downloaded "email" HTML file, then compare the normal message view with Reply; done when the message body is displayed inline instead of only as an attachment.