I am an longtime user but not a freak in using the system. I have the feeling that ISPs have difficulty in implementing good standards, but Thunderbird as well. I had a sequence of issues and failures and had to repair them by continuously changing settings and now it becomes virtually inoperable. I do not want to spend time in solving all these issues, if expert fora suggests pieces of python code as solution I have to conclude that the system does not work any more. One other problem TB changes apparently so much its own menu structure that that is also not working any more. And solutions given cannot be implemented. Sorry to say, this is immature freaky programming, you need some serious system engineers and managers to repair the chaos. Google and ISPs will anyhow continue with their own interest so Thunderbird should be robust against the outside inconsistencies. My complaint is both for the calender as the mail handling. Sorry to say, I am willing to pay that you could hire good programmers, but the volunteers with proper guiding are possibly better qualified. I hope you can solve the issues - changing fully to another environment implies reorganising my work environment.

Hoping you can recover, success, Lars Venema