Hello!
So I use a gmail account with K-9.
I have a couple of months ago sent an email which had a very long header, and ever since I did that whenever I try to look at my sent emails from that account the app crashes.
I think it happens because the app can’t handle that very long header of that email that I sent, also it has been crashing since I sent that e-mail so that furthermore reinforces my thoughts regarding this issue.
The e-mail looked like this (I screenshotted it from the browser page of gmail):
Thanks in advance!
Welcome @ergepard 
Can you please record a debug log, so we can have a look at what’s going on exactly. You can find the instructions here: LoggingErrors · k9mail/k-9 Wiki · GitHub
Unfortunately, when exporting a log from inside the app, it won’t contain information about the last time the app has crashed. You’ll have to connect the Android device to a PC to record a log while the app is crashing.
Okay, no problem.
So now I was able to load in the sent mails folder but it crashed when I tried to refresh it.
Edit:
“[Gmail]/Elküldött levelek” in the logs translate to “[Gmail]/Sent mails” in English.
I still can’t see information about the crash in the log. The message “Wrote stack traces to tombstoned” is an indication that there was a crash in native code. However, K-9 Mail itself doesn’t contain any native code.
In many cases an error like this happens if the app got corrupted somehow. Can you try uninstalling, then reinstalling the app?