Not sure why you copied the ImapMail because any existing imap account would synch with server and get all the emails anyway. Any imap account not in the old profile would need to be created as new imap account in order to get that account set up in prefs.js file.

The 'Mail' folder could be copy pasted, but you would have needed to Exit Thunderbird first, then delete the original Mail folder from profile and finally paste in the copied 'Mail' folder - thus replacing it with the updated copy.

You mention 'Yahoo'. Are all those yahoo accounts using Imap ? If yes: Yahoo uses 'Authentication Method: Oauth2' for both incoming and outgoing server settings. Please confirm that all four imap yahoo accounts have been set up to use 'Authentication Method: Oauth2' That would be for both incoming and outgoing (where you should also have 4 outgoing smtp one per email address)

Assuming all four yahoo imap accounts are all using OAuth2:

If you have imap accounts that are not correct, then I suggest you try this first - reset the saved passwords but do it one account at a time.

please note all your yahoo accounts should have unique passwords, so if that is not the case then please do this now - access Yahoo webmail account via a browser and reset password for each yahoo email address so they are different from each other.

Then in Thunderbird

• Settings > Privacy & Security
• Scroll to Passwords section
• click on 'Saved Passwords'
• click on 'Show Passwords'

Do one account at a time so you do not get confused regarding accounts. For an imap yahoo account which is getting the wrong emails: Look for any line that mentions the 'Username' = email address of that account. Remove all lines that mention that email address/username whether they start with 'oauth://yahoo account.. ' or 'imap://yahoo account'...or 'smtp://yahoo acccount....' click on Close

Exit Thunderbird Wait a few moments Start Thunderbird As one of your Yahoo accounts does not have a stored password, you should get a prompt by Yahoo to enter password for the account in order to allow access by Thunderbird to your account to get emails.

Then access the Saved Passwords again and repeat the same process for any other yahoo account/email address which is receiving wrong emails.

Please report on whether resetting passwords and oauth tokens sorted the issue.

YES that solved the problem, thank you. Note that the passwords for both accounts (the account getting correct emails and the second account getting only duplicate emails from the first account) were not shown in the Tbird 'Passwords' section as the passwords I normally use but instead were [what looked like] a string of random numbers/letters.

Anyway, now the Inbox for the second account has repopulated with all the email messages that were in there before the mixup, and with none of the messages from the first account.

I guess I was unaware of how iMap works. Apparently all messages are stored on the server and then synced with your email client. Which brings up another question. How can I save the iMap email messages permanently on my computer hard drive in the event that they are deleted from the server?

I guess I was unaware of how iMap works. Apparently all messages are stored on the server and then synced with your email client. Which brings up another question. How can I save the iMap email messages permanently on my computer hard drive in the event that they are deleted from the server?

Copy any messages you want to keep permanently to a local folder. You could even create a message filter rule that does that automatically, though you'll end up including stuff that you may not really want to keep.