Thunderbird 115 "Supernova" - constant crashes and now Thunderbird won't boot

[Obbsserver]

I agreed to an upgrade prompt for Thunderbird 115 last week and it doesn't work. It keeps crashing. But worse still, now it won't boot. Does anyobody have an alternative to Thunderbird which will let me import my messages (many thousands of these, needed to comply with the 6 year legal retention rule and for other reasons). Thanks!

EDIT: I found there were numerous instances of Thunderbird "running" (in the background) and after I had closed them I was able to open a fresh instance which is now working. But the crashes of this latest version have shaken my confidence in what is probably my single most important application and I do want to know if there is anything more stable and reliable.

[Obbsserver]

Thunderbird 115 crashed again this morning, twice, while i was checking my emails. the first time when I was moving an email between folders and the second time when I tried to delete an email. It locked completely. I had to go into task manager (Windows) and click on "End Task", then reboot.

[e23w]

I have had problems with crashes for many weeks on an installation with multiple accounts. The solution for me has been to set the connection security to SSL/TLS on all accounts. Now everything works perfectly.