Let's talk about what you hate and what can be done to change it. The reality is old versions are inherently less secure and Thunderbird profile per install makes going back quite difficult, it is not a simple or reliable process. Basically if you could not find the information for yourself on this forum, where it has been repeated over and over for the last 3 years of so, you probably lack the skills to successfully revert to an old version.

Going back without loosing data of some kind almost impossible, even for the most technical savvy folk it is a struggle The process is covered in my blog post of 2019, but I do not recommend it as a process because you do not like the new version. In that instance I was trying to recover lost profiles, which yours will be after you install the old version.

First of all, I want to thank Thunderbird and Mozilla for providing a mail client that was an awesome alternative to Microsoft Outlook and Gmail, it has been great for many years, (10+),

But.... I must share the feeling of the vast majority of the users (I took a few days to check forums/reddit/trends, and the number don't lies...). You want a list of what's wrong ? I'll make you a list of what wrong but please don't attack me and/or blame me for it, I am just doing exactly what you are asking :

- Forced new un-intuitive theme upon users, with no options to keep classic look of thunderbird: This create a whole nightmare for those who write procedure and guide for their users who use Thunderbird. - New version is just as unstable to move large amount of email (15-30K+ email at time), but 10x slowers - The menu bar is misplaced, do not respect UI standards, require complicated CSS override that users don't have time to mess around with. - The facts that all these new changes aren't just comestic and can't be reverted without affecting the "security" of the software, show that "new features / new PR Image" was prioritized over stability and functionalities, and thus respect to SMB that use TB. - The constant denial and the "that what you are stuck with now, deal with it" kind of feeling, leave a sour taste... - I would actually pay a small fee, like 10$ a year per device, if thunderbird would bring back and provide an ESR version of thunderbird that aimed at SMB, and that wouldn't have all the clumsy change that is being pushed to current users... a version that is clean, lite, no fancy or ugly theme stuff (if we don't want em, don't try to push change to us like Microsoft do with their win10/win11/win12) and no menu bar and others buttons change or a way to keep the "comestic" or "UI" that we want (read: need) which should be 100% disconnected from the core code, and have 0 impact on security... - There should be more deployment options with the MSI/Orca and have more documentation with it for a SMB mindset. - Perhaps you guys could collaborate with the EXIM team to create a functional 2FA system or standard and writes from RFC, before all technological insurances company force us to switch to Outlook due to the lack of 2FA in standards IMAP/SMTP accounts.

There a list to start with, I am pretty sure that lot of people will relate too