Best email client I have used and still using on Windows no kidding. Would like to help and will try to make some spare budget.
TBH I won't blame them (or at least not harshly
) if they make a paid version for Thunderbird as long as it's a real permanent license and not expensive, or truly affordable subscription.
I feel it kinda ridiculous for some software developers to claim a "Lifetime license" but in the end, that just lets you use it for a specific version/patch, if you auto-upgrade, then sorry your license is not valid anymore. (Well, this happens a lot on macOS, I don't know the necessity and reason). Further, they just release new versions/patches every year. In the end, either you just stick to the older version forever or "subscribe" to the software. Typically, Iobit, Ashampoo, and many others. (Yep, I paid for a lifetime license for Iobit Uninstaller, and it's not compatible after I updated to a newer version. Took me a long time to get the older version installer, as it's not available on the official website anymore). What's the real lifetime license I was thinking? Adguard, or Windows. At least you could upgrade to a newer Windows version without paying extra money (Win 7/8 -> Win 10 -> Win 11). Partially Office as well. Although you have to pay for a newer version, Office is something a lot of people have to use intensively for work every day, whereas for some other paid software, you might just use it few times every month. Needless to say, Microsoft does not release a new Office version every year. Considering the usage frequency and payoff, Office could be even cheaper. Also, those other software may have a subscription option, but the price, hmm, maybe better just find free alternatives.
Sorry, the above might be a little off the topic. But I just wanted to say, that Thunderbird could be the kind of software truly worth the money you paid, compared to some other software just ripping people off.