Many a true word spoken in jest. Personally I can't see the point of taking existing software, whatever it is, and just changing the name and a few other minor tweaks. Likewise writing something from the ground up when other things already exist would also be waste of resources. So the big question is: Does the world need an Android version of Thunderbird unless it's better than the other existing e-mail clients. As it is why would I, or anybody, benefit from using Thunderbird instead of K9 or vice versa?
I was perfectly happy with the Outlook app for e-mail on my Android devices — apart from it being so big — but the versions that are old enough to work on Android 5 are too old to use OAuth2 so when that became mandatory I looked for an alternative and settled on K9.
I never liked it in part due to the messing about with folder classes, which I believe the Thunderbird version has now removed. Neither could it be made to display folders in a collapsed state so the list was very long as every sub-folder was permanently on display. The picture on the right below shows what K9/Thunderbird can't do — or couldn't when I tried or I couldn't work out how if it is in fact possible.
I never could get it to work how I wished, though can't now recall details, and contented myself with having something that would bleep if an e-mail arrived when I didn't have a computer switched on. If the message needed any more attention than deleting or reading I'd switch a PC on to do it.
I tried Thunderbird a few months ago and couldn't tell a difference apart from the logo and nicer colour-scheme. It seemed even less configurable than I remembered K9 being and I wondered if options had been removed to reduce the number of variables whilst it was in its testing phase. That could well by my memory deceiving me though.
That got me again looking for alternatives and that was when I discovered FairEmail.
I agree that FairEmail's host of options can be confusing so ideally it, and Thunderbird, would take a leaf out of VLC's book and by default only show basic settings but have an 'Advanced Settings' button that shows the others if needed/desired.
For an Android version of Thunderbird to have a meaningful purpose it would need to be as similar to the desktop version as possible given the restrictions of Android devices so my familiarity with that would count for something.
I've always found that there is some software that I simply get on with and some I don't. FairEmail comes into the first category and, sadly, K9/Thunderbird the latter. Objectively why is difficult to pin down.
