Your post gives the impression that you are new to Thunderbird, coming from using Outlook. I say that because your comments are laced with what Thunderbird "should do." My suggestion is to focus on Thunderbird's strengths, which are many, instead of comparing to Outlook. I will comment on a couple of your topics:

- setting up POP with Oauth2 for a Microsoft account works fine. I just did it to verify, and the popup from Microsoft appears as anticipated. - on switching from IMAP to POP: this is done by creating a separate account. This is required because the underlying architecture for each is too different to simply change settings within an account,

Hi!

Ok, I managed to install one of my old MS Accounts as POP3 with OAuth2 now, perhaps it worked due to me updating TB from 115.12.2 to 115.13.0, whom knows.. Anyway, the PopUp Window DID occur this time.

(And I got TB whenever it was Gmail demanded OAuth2, a year a two ago perhaps?, and I can't recall having to authorize in a PopUp window back then?! Since I added quite a few Gmail accounts, I think I would have remebered such an annoyance.)

But I just must ask why that PopUp Window is necessary in TB, when it's not if using the "new Outlook for Windows for free" ?

https://apps.microsoft.com/detail/9nrx63209r7b?hl=en-us&gl=US

When one enters a new email and password in "New Outlook" no extra window asking for permissions ever occur. (I don't like that prg for many reasons, but I just think it's strange it doesn't ask for that permission that TB does.)

And I just found an interesting possibility! One can click 'Go Offline' down at tha bottom bar, and then a question about Downloading All Msgs appear. That's great, if it means that all msgs are kept in TB for ever, is it so ?! Since that would mean that even an IMAP Accounts msgs will always be available local!

/Thanx so far!

On your comment about offline. For IMAP, you should - go to settings>synchronization&storage to verify that the folders are set for offline access. - click file>offline>download that will download all messages so you can work offline with them, but that does not mean they stay downloaded forever. This is because IMAP architecture remains focused on the server, not the PC. However, after doing the download is a good time to do a backup if you want all messages archived occasionally.

Ok, that were a bundle of MS Accounts done...!

And after both Gmail and now MS Mail, it's probably time to do also all the different Yahoo accounts, such as Yahoo.??, Ymail.com, Rocketmail.com.

Do TB recognize those other Yahoo domains?

Already 2020 Yahoo forced everyone to start using a 16-Char newly generated password:

"You can generate a one-time, unique password that will allow you to sign in to your account using your non-Yahoo email application. Once created, this password will continue to allow your app to securely sync your Yahoo email unless you sign out (or are signed out) from your app."

https://uk.help.yahoo.com/kb/new-mail-for-desktop/learn-generate-third-party-passwords-sln15241.html

(But if one signs in with a Browser, the old fashioned password still works.)

And Yes, You're right about BackUp, but Where does TB keep the DATA files, and Where does it keep the Email files? (I'm on Win10)

/Thanx again!

all files are kept within the profile folder.

Ok Thanx, but WHERE/in what Folder on the Hard Drive are those files (the Data and Mail files) kept?

And, is there a way in TB to add ones Own Name to an Account, like one can do in Win Live Mail, (SEE the image) where it says: "Type the name by which you like to refer to these servers"? I've added 'POP3' or 'IMAP' after each of my accounts, and then this my Own Name is displayed in the Accounts Listing to the left of the screen.

And What is this Blue Line to the right of the bottom of TB frame, SEE Image!

(Strange editor here, I would like to Place those 2 images after the sentence I've written, but that doesn't seem to be possible?!)

/Thanx Again!

you can find the exact location this way: - click help>troubleshootinginformation - scroll down left side to 'profile folder' and click 'open profile' - note the hard drive location as shown within windows file explorer. - IMAP accounts are in the Imapmail folder and POP accounts in the Mail folder and local folders are in the Mail\Local Folders folder

you can set account name in 'account setting' in the field called 'Account Name' I do not have the blue line. It may be an attempt to reflect usage against server quota.