Hi KevinTheJedi
Okay, As you suggested.. I have deleted all other mails and kept only one mailbox. The below screenshot for your reference.
But the error is still the same.
No, NEW mail on configured mailbox.
new mail sent on target configured mailbox - INbox screenshot for your ref.
Run the cron and still same error and mail got read on Gmail
And as an Admin, as usual I do received error notification as well.