I cannot duplicate that. What is your version number?

102.9.1 (64-bit I did find where to do that, but now if I click on any message, it opens the whole thread - not really what I had in mind. I already set it not to show messages as a thread. Now it opens 50 Windows.

Did your setting for that folder show that the view is unthreaded?

I did every single one of them. Also, since I have you, it doesn't allow me to import anything from a PSY file; it's grayed out. Messages are fine since they were IMAP, Calendar, and contacts not. Somehow MS forced me to switch from POP to Imap, and I have a lot of backup PST files, which I do want to use in the future without resorting back to Microsoft Outlook, or a third-party tool.

I wish I had a magic answer for PST. I did locate a freeware utility that converts PST to EML and Thunderbird needs no conversion for eml. The freeware is at https://www.outlookfreeware.com/en/products/all/OutlookConvertPST2EML and you could use the importexport addon to import them into a folder. I know of nothing else that can convert without Outlook or without a fee.

Thank you. Outlook 365 only exports to comma delimited or PST. I'll figure it out. Thank you for being so helpful!