External IMAP Accounts Issues

[merrickville+zimbra]

Good day.

Version: Zimbra 8.8.12_GA_3809 (build 20190614033345) on Ubuntu Linux 18.04 LTS
Browser: Firefox 67.x x64 Windows 10 and Ubuntu 18.04 LTS / Chrome / IE 11

I have created 2 external IMAP Google Mail accounts under Zimbra Preferences / Accounts.

One of the Google email account works through Zimbra, the other one does not.

I enabled the 2 Step Verification [2SV] on the account that does not work, and generated a Google "App Password" (Less secure access to Google)

When I put this "App Password" in Zimbra, that non-working account works!

Unfortunately, to use Google's App Passwords, you also need to enable 2SV. Where I work, I'm have no access to my phone for the 2SV, and to compound my issue, my mobile number often requires two or three "Resend Verification Codes" before I even get one. Therefore, I must disable 2SV, and loose the App Password generated by Google.

I have reset the non-working Google email password to something new. Google says it is a "Strong" password. I enter this new password to the External account that does not work, yet I consistently get a pop up: Error: Invalid credentials (Failure)...

Both external Google email accounts have identical server settings, (except username/email address and password), one works, the other does not.

I'm thinking Google has flagged this one account as needing "Less secure access to Google" ??? But for the life of me, I can't understand why this would be the case, I use both email accounts regularly on other devices without issues.

All my other email clients willingly accepts the new password I've set. Yet I continue to get the Invalid credentials when I try to access the same account via Zimbra.

I'm also loath to contact Google Help, they say it could take up to 5 days for a response! Wow. So, I ask here first.

My guess is, Google has flagged my email account, and somehow fingerprints headers and such detecting that I'm accessing from Zimbra and shuts me out.

Anyone have an idea on what could be happening in my situation? Is my previous sentence the answer?

Thank you.