Original author of K-9 here. I haven’t been involved in the project for some time, but my recollection is that any time we investigated this issue, we found that the issue was GMail displaying multiple drafts to the sender as having been sent, not actually sending the drafts via SMTP.

(That’s what the bug reference in a reply to this comment is about)

Yes I actually faced this exact bug myself a week ago. What happened was - my mobile app gmail displayed my draft as sent (but actually I have already completed it and send it using desktop web app), but when double checked on desktop, it indeed actually send my completed email, not the draft.

I tried restarting the app/ refresh email threads, but it didn't fix the visual bug. I'm not sure if the bug is still present today as the email thread has been buried down and I couldn't care enough to follow up on it. I'm just glad it didn't actually send my draft when somehow the app displayed my draft version as sent.

Note that I'm not a user of K9, I'm just describing similar buggy encounter with Gmail desktop and its android app. I only noticed this that one time and just shrug it off due to me turning off apps auto update. Usually I only update manually when I really think I need to and after carefully reading each change logs.

This appears to be still an open issue. https://github.com/k9mail/k-9/issues/2060

I just tested it. It saves a draft each time I switch the screen but when I press Send only one email is delivered (the last one, as expected).

That's horrifying. I imagine the moment you found out a cold wave went down your spine.

Wow, you've tarnished that client's reputation forever in my mind. How many "drafts" went out?

A massive killer for me was sending mail under one username but indicating others in body and headers.