Auth 2.0 Error 400 on Mail account

This worked for me:

I noticed that the popup to login into google, when trying to add a new account, was opening in Safari Private Browsing mode. I went digging in Safari's settings, and in the "Advanced" tab under privacy I turned off the "Use advanced tracking and fingerprinting protection" AND the "Allow privacy-preserving measurement of ad effectiveness" and BAM... I was finally able to get past the 400 error that Google was sending back and I was able to authenticate and add my Gmail account to my Internet Accounts.

I'm not sure if it is because I'm running High Sierra, but I did not have "App Passwords" as an option under the "Security" tab. So, while logged into my google account, I went to:

https://myaccount.google.com/apppasswords

and followed the prompts. Write the password down. Copy and paste did not work.

I then deleted the mailbox in the Mail app, and added the new one under type other with the gmail address and the new password. Everything repopulated with no hitches.

Thank you, The Animaster. It has resolved my problem and extended my Macbook's lifespan by a few years. I would like to add some details that could be useful:

• For some reason, the "App Passwords" section did not appear on my "Security" page. I could only access it by searching for 'App Passwords' in the Google Account search field. If your Google account language is not set to English, you must search for the exact string used by Google in your language for this section (e.g., 'Mots de passe des applications' in French).

• After creating the new password: In Apple Mail, as The Animaster mentioned, make sure to select 'Other' when adding the new email account (you'll need to manually enter all Gmail information). Choosing 'Google account' will result in the same error 'You can't sign in to this app because it doesn't comply with Google's OAuth 2.0 policy for keeping apps secure'.

Good luck!

I did it yesterday on High Sierra and it works.

You need to delete (not just deactivate) the "original" Gmail account before adding it back with "other mail account" .

Then use the "app password" provided by Google and voilà.

I cannot remove this old account otherwise it would be removed from all devices including newer ones.

I don't think so. Your Google account won't be deleted or removed on other computers.

One more thing : I tried to do the same and another old family iMac stuck on Sierra (last authorized OS) and it didn't work counter to the High Sierra Mac. Still seeking for a solution for that one :(

I have had this problem adding a gmail account to Mail. If you go to google help and describe the problem they will suggest a 16 digit app password that they will generate. Then go to add accounts in Mail. Do not click on the google symbol click on other account which you see when you scroll down, fill in your google data (email address) and use the generated password. It worked!

I seem to have fixed my issue: I found this page How to download and install macOS - Apple Support

and have managed to download and install a later version of OS (Catalina) manually which has allowed my Gmail accounts to link to Apple Mail again.

I'm sure they will fall down again soon as Apple say my machine doesn't support Catalina, but it will hopefully give me a few weeks to research a new machine, rather than a rush purchase.

My Word and Excel for Mac no longer work with the new OS, but they are as old as the machine (2013) and I'm being directed to use Microsoft 365, so I'll have to see if I can find a workaround for this now.

I first asked for Gmail in the 'App Password' dialog box

I still had the same problem.

Then, realized the Apple App is called Mail

I asked for an 'App Password' for Mail

and voila... it worked.

Yay!! and Thank you!!! my emails are downloading as I type this

Currently the only solution is to download the "mail for gmail" application from the appstore. This way you can use your gmail account even on old mac os.

In my case (old Macbook Pro, late 2011) I generate on google account separate password for app and then i the Mail add Other mail account. With regular pass for gmail won't work.

Animasters procedure worked for me on my MacBook Pro with High Sierra after figuring out two additional steps:

3a.) "app password" did not show up for me, but I could search it with the search bar on top which brought me to the page mentioned in 4.)

It didn't work right away, I got "password could not be verified" various times, until I had switched on "activities" in Google safety settings (not sure that bit was necessary, I changed it again after everything worked) and then clicked on the "check activity" button in the safety/confirmation email I got from google on my secondary email account regarding the creation of the app password. After that, the account was confirmed.

thx for the help!

This worked for me so much appreciated. I removed my Google account from 'Internet Accounts' first (as could not sign in) before adding it back under 'Add Other Account' as you say with the newly generated password from'App Passwords'. I am using High Sierra 10.13.6.

Search for “App Passwords” on top of the page and create one for mail.

It works! In Security options go to two step verification to find App passwords.

Hi Guys, I managed to solve everything!

I have Macbook Pro 2011, Hig Sierra.

My steps were as follows:

1) I left the old gmail account disabled which didn't work.

2) Thanks to the system indicated above I logged into my Google account and created a new password for MAC and Mail.

3) On the Mac, in the mail app I created a new account by choosing "other" and writing my email with a dot before the @ (example: mymail.@gmail.com)

4) At this point I verified that the new account was working properly.

5) I re-enabled the old GMAIL account which no longer worked and... as if by magic it started working again!

6) At this point I deleted the new account I had created thanks to the "others" function

The old GMAIL account works fine!!

[Edited by Moderator]