K9 is sending false “Read” receipts. Read receipts are being sent upon delivery, well before being read. “I have a Read Receipt that says you read my email!” “Ahh… Nope. I have not even opened my email yet today…”
Welcome to the forum 
K-9 Mail currently does not support sending a read receipt. The “delivery receipt” is most likely sent by your mail server when it receives the message. See Return receipt - Wikipedia
Contact your email provider. It’s possible that they don’t offer the option to turn off those delivery notifications.
Did you see my screenshot?
There’s read receipts and there’s delivery receipts. They’re not the same thing.
K-9 Mail does not send receipts of any kind. Please contact your email provider to find out what’s going on.
As cketti (prior K9 lead developer and project maintainer) stated, the app does not send read reciepts. The core developers know the app intimately so you can be confident in their answer.
I’ve also searched github and there’s no pull requests implementing the feature, either before or after Mozilla took over stewardship of the app. There was some discussion in github ticket #1432 about adding support but it never moved forward.
As others have said already: K-9 Mail does not send read receipts.
- Do you have some other MUA (email client), maybe on some other device? It might be the culprit.
- Look at the email headers of such a read receipt, where you see a lot of technical details about the email and it’s delivery path etc. Compare those details with the email headers of an email you sent from K-9. Feel free to DM me if you need help understanding the headers.
Have you looked at the content of the ‘noname’ attachment in your read reciept.
My provider attaches a similar sized MDN text file containing among other things, the user agent of the client that sent the response (Reporting-UA:).