It may be possible by directly editing settings files, which is non-trivial and all too easy to get wrong and break Thunderbird.

But why bother? With a well known provider such as Google it's easy to set up an account afresh. And you don't need to know anything other than the email address and its password.

Or just take a screen shot of the relevant settings pages for the existing account and enter them by hand for the new account. But this is actually more work than setting up the account from scratch.

I think with Gmail in particular you will still have at some point to do the OAuth2 procedure, or will have to enter an app specific password, or use two factor authentication. There is so little to gain by trying to clone an account that no-one has thought it worthwhile to write the code.

Are there any particular aspects of the existing account that you specifically wanted to transfer to the new account?

Not to mention copying the SMTP settings to all accounts and then coming back asking why I sent email from account B but it shows it came from account A.

I have several Gmail accounts. Once I get the Thunderbird settings the way I want them with the first account, I will want to Copy/clone/duplicate them repeatedly for the additional accounts. It is a common way of doing things when multiple accounts are involved.

To answer your question, I want to copy ALL email account settings (there are many) to the subsequent new email accounts. Yes, I could screenshot all the Settings dialogs but its so easy to miss one of them.

I did not ask if this was reasonable or not, as many other users have also asked this question.

Airmail said

Not to mention copying the SMTP settings to all accounts and then coming back asking why I sent email from account B but it shows it came from account A.

I understand I would, of course, have to update the User Name for each account.

Again, I ask, what particular settings do you have in mind? I suspect you are thinking beyond just server settings.

Yes, I am thinking beyond server settings. I am thinking ALL SETTINGS. When I am satisfied how TB accesses this initial Gmail account, then I am hopeful I can clone/replicate ALL SETTINGS to the other Gmail accounts. I realize, after cloning ALL SETTINGS, I will have to manually change the UserName and Password for each new Gmail account.

Is there a reason why you have not just created a new existing mail account for for account2 which would auto create duplicate server settings using the new Username which is obviously a new email address with it's own password? 'Menu icon' > 'New Message' > 'Existing Mail Account'

Are you talking about imap or pop ?

I think this is about user preferences, such as default folders and the columns in them, default settings for copies, junk etc. Maybe filters, default address books for junk recognition, synchronisation. All that tedious stuff you need to do when adding an account and trying to make it consistent with all your old accounts.

Setting up the servers and connection is only the smallest and least tedious part of it.

Toad-Hall said

Is there a reason why you have not just created a new existing mail account for for account2 which would auto create duplicate server settings using the new Username which is obviously a new email address with it's own password? 'Menu icon' > 'New Message' > 'Existing Mail Account' Are you talking about imap or pop ?

Thanks Toad-Hall. I am talking POP. I was not aware that creating a second account would automatically copy or as you say 'auto create/duplicate' default settings from the first account to the second account. If this is in fact how TB works that sounds fine.

I don't think "duplicate server settings" will help the OP. I think she wants all the other user preferences to be cloned. It would be non-trivial to code, as they are split over prefs.js, the various *.msf files, and perhaps some .json files.