Hello. I am aware that I will probably have to jump ship on Mac Mail after this experience; however, I wanted to put this out there in case others have had similar issues. I recently updated my 5,1 Mac Pro to Sierra. Overall it didn't break that much stuff. The biggest problem by far has been with Mail: 1. None of my Gmail accounts will work without turning off Google's protection against "Less Secure Apps". I don't want to turn this feature off as it assists in protecting my account. Furthermore, there was no need to do so on Mavericks with identical settings. 2. For accounts that have 2 Step Verification, I don't even have the option to turn off "Less Secure Apps", and am therefore unable to continue using Mac Mail with Gmail securely. That means that I have to use double less protection (no 2 step verification and no protection against less secure apps) to get Mac Mail to work with my Gmail accounts that were fine a week ago. This all worked fine in Mavericks WITH protection against "Less Secure Apps" turned on! 3. The password field in Mail Preferences is gone. I mean, it is literally gone. Even if I go into server settings it is not there. What kind of joke is this? Are the employees at Apple stupid, or did they seriously intend to remove this without adequately replacing it? I am aware that if I try to send an email from an offline account, it brings up a pop up window where I can dig into the servers and find a password field. BUT, since Google's solution to this Mac Mail nightmare is to use App Passwords, how come when I finally put in the App Password to this evasive password field, it doesn't work at all??? EDIT: Internet Accounts did the trick... why in the world there is zero indication of this while stuck in a nauseating loop trying to fix the problem in Mac Mail is beyond me!