Game-changer... how? There are at least two players in email space that provide encrypted email and various auxiliary suites (Protonmail and Tuta), plus at least one well-trusted well-respected email service (Fastmail), and of course people can always self-host if they dare. What revolutionary they could possibly realistically bring in areas privacy and security to be an actual "game-changer"?

Not saying it cannot possibly be - just that I cannot think of any novel way how it would deserve a title like this in such a particularly tricky niche as email suite service.

I've used Thunderbird for years and know half a dozen other people using it, including one who has folders with tens of thousands of emails, and have never heard of any data corruption.

Thunderbird is my daily driver email client for all my business email for over a decade.

I've never had a single corruption problem in that time, with probably hundreds of thousands of emails. Take that for what its worth.

The only complaint I've ever had is when they redid their UI a year or two ago it got unbearably slow - which improved over the next few iterations until its now fine again.

My coworker uses thunderbird since time immemorial, and I don’t think it ever corrupted his mailbox.

I have been using Thunderbird myself for years and never had any such problems.