Let's put this in perspective... allowing that the number of daily Thunderbird users exceeds 10 million. Then look at the number of users of the 10 or 20 most popular addons. The first 20 gets to less than 30,000 users. Of those 20, Three are not available for the current release (78). Of those three, one is Lightning which is inbuilt and another in the importexporttools which the author unfortunately decided to stop supporting and was replaced with he importexporttoolsng (also in the top 20)

Certainly an update can cause disruption, it can actually be disastrous for some. But just because you consider an addon essential, there are millions of other users that have probably never heard of it.

It is an unfortunate or fortunate (depending on your point of view) that thunderbird is locked into being built on the mozilla platform. This means that Thunderbird is locked into fundamental changes that Mozilla make to the platform. Mozilla decided to adopt webextension for addons to match Chrome, Thunderbird had to go along. Moving was not optional, the code that supported the old style addon was removed from the Mozilla platform. That web extensions were not really suitable for a fat desktop client was irrelevant to the Mozilla position. They ceased development on Thunderbird years ago. So the Thunderbird teams expanded on the web extensions and called them mail extensions. The result however was that over a couple of years the way extensions were written completely changed. Many folks involved in extensions were not in a position, or unwilling to invest the time in a complete rewrite.

That is how it is, there is little or nothing anyone could have done to cushion the transition any more than the development team did. They did manager to make the big bang stretch our over years to give time for updates that was not available to Firefox addon authors. My chose not to continue. That was their right.

Now lets look at something else you mentioned. Funding. How much funding is enough? To get a quality product, $10,000 is probably a low starting point. Software development is expensive. Good quality development even more so. Thunderbird developers have another cost advantage, there are not many of them.

I do not disagree that there are many functions the program lacks, but my top list including import/export of settings and data to a new device, and an account settings checking utility are probably nothing like yours. I think we will find almost as many top 10 wanted items lists as there are users really.

Dear Matt, thank you very much for your letter. Look, if there are already more than 10 million users, this means that the program is popular and in demand in the market. This means that you can already make it paid, for example, a one-time purchase for a reasonable price or some cheap subscription. But making it paid is probably hindered by the confusion - who owns it, who owner of the trademark, etc. As for the program's operation itself, yes, I agree that updates are constantly required. But there are things with which the program works better and more comfortable for the user. In our situation, these are add-ons that enthusiasts and amateurs create. And if you look at all the add-ons that are offered for use, then, in my opinion, 95% is something that few people need— very specific stuff. I'm talking about add-ons that almost all users use. Moreover, in the comments to such add-ons, users ask a question - why don't the program developers do it? And after each program update, users swear - why does the necessary and useful add-on stop working? So, suggestions are immediately apparent - the program should (and work with any update) add-ons from the series "must be." If you can't make the program paid, why not make add-ons paid? Who is stopping you from doing this? In this case, the program will be updated, addons will work, and users will be happy. Is it easy to do it? I think yes, engineers can tell you how to do this. Second, I believe that Thunderbird needs a designer because the program's design remains at the level of "yesterday."

There are a number of paid addons. For example https://addons.thunderbird.net/en-US/thunderbird/addon/owl-for-exchange/?src=cb-dl-users it is not alone, but is one of the higher profile ones as it is basically needed for office 360

But no one can make the author actually charge for their work and no one can make them continue to maintain them.

There is considerable work being done in the UI. With a UI developer having been employed thanks to user donations. Perhaps you would like to follow the various discussions here https://thunderbird.topicbox.com/groups/ux This is not the place for that.

Funny example, see what you have to offer: https://addons.thunderbird.net/en-US/thunderbird/addon/owl-for-exchange/?src=cb-dl-users it says that after your update the addon does not work :))

I am very sorry that we did not understand each other. If I find some mail program that is acceptable to me, I will part with Thunderbird without regret. I have a problem - I don't know enough technique just to transfer all my letters/mail. I hope that I will either figure it out myself, or I will pay a specialist. Thanks for your participation and good luck!