Lets start at the beginning.

You did not have to delete anything, just change the authentication method used in account settings. The same dialog you would have found the account actions button in.

See http://kb.mozillazine.org/Recovering_deleted_mail_accounts

OK your solution led me in the right direction. My heart was sick thinking i deleted 10 years of emails.

The issue was that my old email was a POP account. When i re-added the account it was an IMAP account. Google is forcing people to upgrade security which is breaking POP accounts. In thunderbird POP accounts there is NO Oauth2 Authentication Method. This forces people to use IMAP and keep all their emails on google's servers.

So now I've re-added a POP account and changed the local directory to the old POP account which was deleted. But this account is no longer updating anymore. The new IMAP account is now updating with the new emails to my gmail account.

Do you know of a way to use Oauth2 with a POP account? Also had i pointed my IMAP to the old POP local directory which sits in the Mail vs ImapMail folder would all of my old email show up without it all being uploaded to google's servers? Hope this makes sense to everyone. If not please let me know.

Google is forcing people to turn on "Oauth2" authentication method which is only available in IMAP. I like POP accounts because keeping things on google's server over 6 months is not good hygiene but google security checkup is saying that the "Normal Password" authentication method is not secure. So you must use IMAP to pass the security checkup. I also have developed a rich folder hierarchy in my pop account which would be lost when transitioning to IMAP. Not sure what would happen if i pointed my new IMAP local directory account to the POP account local directory. First issue is that Thunderbird stores IMAP in the ImapMail vs Mail directory. Not sure of any other structural issues. Also am assuming all the POP emails would load to google's servers. Believe the sync issue solves nothing because it just mirrors a local copy of the everything on the server.

If you insist on passing Google security checkup your POP account will stop working. I fail their test all the time and now I ignore the stupid email they send out. Sorry google but the more email you send me the lower your credibility in this becomes. I tire of their political agenda here. The truth is that oAuth is a web authentication method, making it a mail requirement requires all mail clients to basically act as web browsers for the authentication to occur. So while it might be technically more secure. I am not convinced having mail client developers working on web browser feature is actually more secure over all. Not that it makes a lot of difference on Android, the only thing they really care about because apps on Android are basically web pages anyway.

I did submit a bug report asking that oauth be allowed for pop. https://bugzilla.mozilla.org/show_bug.cgi?id=1538409 It was not an option in the past because Google simply did not support the authentication method for POP, only for IMAP.

You still did not need to delete anything, you chose to. With unfortunate consequences

If you point your imap account to the pop account everything will be synchronized out of existence.

I suggest you choose to fail the checkup, enable less secure apps (which is really not all that true) and continue to enjoy mail as you are used to it until the bug is acted upon. Not that their is really much hurry to do so. Normal password works for me.

Having not much experience with Thunderbird settings, I created a new account since my POP account was not working. I also read a support post stating by creating a new account all the default settings would be up to date. This however created an account which conflicted with the previous account. So in the ensuing confusion i assumed i could create a new account and import the emails that would still be on the computer. Since then i have educated myself on POP vs IMAP and authentication methods.

For the average user, i feel this process to understand this would be daunting. Had i mapped the old POP account without knowing that the new account was IMAP i really would have lost everything. Feel that many users would be hitting this issue. And by making a more idiot proof (not sure how) for this issue would benefit the adoption of thunderbird. So from what you have stated my takeaway is that "Normal Password" in POP is a secure authentication method in today's computing environment. Thank you for your insights. Nice to have an experienced person to provide knowledge to the community.