Is there a way to ditch Thunderbird?

[HopDavid]

I made a donation to Thunderbird awhile back.

And then I was assaulted with a webpage each time I opened Thunderbird.

And then the interface was re-arranged and changed. It took me time and effort to build a system of habits to do what I need. Thank you for throwing that in the trash.

The threading screwed me up. I want messages sorted by date received as the default.

And now Thunderbird is not downloading messages. 

You have made my life hell. 

Can anyone recommend an email app that works? And how do you transfer data from Thunderbird to a new email app?

[ArnoldGreybeard]

Take a look at the SeaMonkey suite. It includes a sane email client with the Lightning Calendar extension built in.

The suite (including a browser) is still being updated but with (so far) minimal changes to the user interface.  Supported on Windows, MacOS and Linux.

Both the main parts of the suite use mozilla code albeit packaged with a stable UI. The browser lags behind Firefox a bit but the email client does everything I want.

https://www.seamonkey-project.org/

There is a legacy mozilla version of uBlock Origin that can be installed and I find that SeaTabX2 is a useful addition. The browser has the tabs in the right place.