re :The problem is when I switch to another user account (windows 10) and launch the software under that account. The e-mail account which existed when I was an administrator does not exist.

Of course it does not exist. I would be more surpirsed if it did show you the account. The User Account called Admin has it's own desktop and set of folders etc. It should have it's own password to access that admin 'User Account'. It will have it's own desktop, documents, emails etc.

When you run Thunderbird in any User Account, a profile is created within that User Account. It is unique to the User Account. The thunderbird profile name folder is located : C:\Users\<Windows user name>\AppData\Roaming\Thunderbird\Profiles\<Profile name>\

This means several users can use one computer. Each has ability to logon to their own 'User Account' using a password that is different for each User Account'.

Thunderbird can run in each User Account and create a separate profile in each User Account. Each profile can have their own mail accounts/email addresses and receive emails from completely different servers. It means different people can use same computer but not share same profile. If you do not know the password to the 'User Account' then you cannot logon to see that desktop, you cannot see any of that users emails nor get access to their stored passwords.

It is the same basic security that all computers offer.

Thanks for your reply. I understand the fact that I am unable to see e-mail accounts from other users. But this does not solve the problem that I am able to create an existing account when I am logged as an administrator but when I log in using an account which is not an administrator thunderbird will not create an existing account when I click on done I get this error message

Not sure whether you are creating a gmail or yahoo account or using Authentication Method Oauth2 , but some accounts do require that cookies are enabled.

Menu app icon > Options > Privacy & Security Under 'Privacy' section Sub section 'Web Content' Select checkbox 'Accept cookies from sites'

Also check - are you creating the same Type of account, IMAP or POP ?

If you try to create new existing account as POP but then use Imap server settings and ports then it will not work and obviously same the other way around, you cannot select Type as Imap and then try to use Pop ports and server settings.

You could Post an image when creating the account, so we could see server settings.

I got it working here is what I did. Logging as an administrator I uninstalled Thunderbird and re-installed from the installer on my computer (version 78.2.2) Started Thunderbird no e-mail account would show. I created an existing account put the correct information click on test it downloaded info from the server I put in the correct user name and clicked on done and I would get an error message (same as before). I then uninstalled the software and installed instead version 68.2.1. Started Thunderbird and e-mail account was there and working. I then switched user (this is not an administrator account) and tried to create an existing e-mail account (new e-mail address) and it worked. I am updated now to version 83 no problems