What you describe works for me.

So…

Operating System? Thunderbird version? Any add-ons? Does it work better in Safe Mode?

Can't answer your questions except that I don't have any add-ons. I don't know how to find which version of Thunderbird I have, don't know about Safe Mode. Adding folders used to be easy, and then without changing anything I can no longer do it.

ingridbroad said

Can't answer your questions except that I don't have any add-ons. I don't know how to find which version of Thunderbird I have, don't know about Safe Mode. Adding folders used to be easy, and then without changing anything I can no longer do it.

Well your also not able to correctly identify your add-ons is my guess..... for the last couple of versions everyone has a calendar add-on installed by default.

For a programs version I suggest you do what has been the standard windows way to get a program version since about 1985. Go to the help menu and look on the about entry.

While you are on the help menu you might try restarting with add-ons disabled from that same menu.

As Zenos says, your procedure works for him... it also works for me. Although "I have no idea why anyone would want folders hanging off their inbox. Perhaps get involved in the diagnostic process that explains what is different about your computer. Other than the fact your using Windows 10.

@Matt, I wouldn't choose to build subfolders under Inbox myself, but at least one of my email providers runs things this way.

Outlook.com/Office365 seems to prefer user folders to be under the Inbox. :-(