Hello, I’ve been using K9 for years, but I don’t like the crappy new design and functions.
So I’ve been using the version “k9 mail 5.600 apk” on my Samsung Z Fold 4. Since today, I have the Z Fold 6 and when I want to download and install the APK file, I always get the message that the file is invalid.
Does anyone have an idea how I can install this version?
That ancient one is probably simply too old to run on modern Android versions. Either do what most of us did and get used to the current one (which is actually great once you get over the loss of the overview screen), or find another app to use.
Very annoying. I don’t understand why a company would simply destroy a proven system and design.
What app alternative is there that has a similar design and functionality to the K9 “old” version?
Download the Android device bridge to you computer and then run:
adb devices
adb install --bypass-low-target-sdk-block FILENAME.apk
adb kill-server
That will circumvent Android 14’s target restrictions.
Thanks for your information, but I have absolutely no idea how to do this?
Sorry. When people continue to use software out of support, I always assume they know what they do and are aware of the risks associated…
You can download the old K-9 APK from Fdroid, fetch a USB cable, and then follow the instructions from Android.com.
But be aware that you will be using outdated software. No security fixes; lots of potential attack and failure vectors.
But the Version 5.600 is not available on F-Droid.
You can use the GitHub version instead. It is functionally identical.
https://github.com/thunderbird/thunderbird-android/releases/download/5.600/k9-5.600.apk
Before you attempted the installation, did you connect to your device using a USB cable and ADB to allow the use of the outdated package?
With a lot of effort and YOUTUBE video tutorials I have now installed it but apparently there is still an error somewhere.
USB debugging is “active” on the Samsung Z Fold 6.
What should I do?
see here as well
The top result from Stack Overflow seems relevant.
Sorry, but I don’t understand what you mean.
I would really appreciate it if you could help me set this up.
I have now installed the latest version of K9 on the Z Fold 6 with 8 accounts and it looks terrible when I always have to jump back and forth between the accounts. With version 5600 I have all accounts at a glance as soon as I open the app.
Click the Brave Search link I shared. Follow the top search result from where a Stack Overflow post explains how to fix the ADB device unauthorized error you are seeing.
The only help I can offer is to point you in the right direction. You still have to do all the work yourself.
My solution to the interface change that occurred years ago was to:
I don’t like running obsolete software. If you want to, then you need to:
You also have to be able to support it yourself, because no one else will.
I have no knowledge of such things. Can’t you help me remotely?
Like @linkp said: “The only help I can offer is to point you in the right direction. You still have to do all the work yourself.” and “You also have to be able to support it yourself, because no one else will.”
Instead of trying to work around Android limitations, why not simply try the current version for a while? It’s actually quite good 
I have no other choice - very annoying.
The current k9 is ok if you only have a couple of accounts. But for those with multiple accounts, the current k9 is a pain in the butt to use.
Like the OP, I tried 5.3 on my Fold 6 but I have been told that because 5.3 (5.6) is a 32 bit version and Fold 6 is exclusively 64 bit, it won’t install/work.
Screen shot of 5.3 before k9 started going downhill.
