Mail and Google's OAuth 2.0 policy

This might be fine if your iMac is a within a certain age but with a mid-2010 or 2011 iMac, running High Sierra 10.13.6 is as high as Apple will allow the OS to go.

I get exactly the same problem as reported above - all my Gmail accounts within the Mail app are suddenly non-operational because I changed the password as part of a security review (prompted by Google) and from this point I have been unable to receive mail to my Gmail account using the Mail app on my iMac. The password field does not appear on the Details screen within the Internet Accounts part of Systems Preferences - I get the following:

You can't sign in to this app because it doesn't comply with Google's OAuth 2.0 policy for keeping apps secure.

You can let the app developer know that this app doesn't comply with one or more Google validation rules.

So I am letting the app developer know so that Mail can be updated to cope with it...and asking for this upgrade will be available to users of Mail on High Sierra. Currently I am running Mail v 11.5 (2018).

The only workaround I can use on the iMac at the moment is webmail.

I just went thru this myself with two sessions with Apple Support. We tried multiple attempts to fix my gmail account in Apple Mail after a gmail password update. I finally deleted the gmail account from Mail and tried to re-add it, also with failures.

For me, the solution was in 'System Settings/ Desktop & Dock' and set Google Chrome as the default browser (I had to download Chrome and install).

Hard to believe that Google is so petty that you HAVE TO use Chrome to authenticate your addition of gmail to Apple Mail after I updated my password in gmail. Google gives no indication of the failed issue when using Safari (a "400" error with a snarky comment). There is a reason I am getting rid of my Google accounts, apps, etc.

Rat Finks! [They know]

Try this...

Mac's Mail App is not as modern as iOS's Mail app, Many eMail providers now require a separate App Password different from your eMail password…

It may just need an App Password separate from the gMail password…

https://support.google.com/mail/answer/185833?hl=en-GB

Apple Mail won't sign in to Google account - Apple Community

Note from PrestoWebDesign…

Trying to add Gmail account to Apple Mail… - Apple Community

If using operating system 10.13.06 (High Sierra) or earlier, that is the problem. Some computers like my 2015 MacBook Air were compatible with a newer MacOS but hadn't updated for lack of enough free storage. Cleaning out junk files gave me enough storage to download 10.15.7 (Catalina) and the problem was solved with the newer built-in Mail app.

See if your computer is compatible with an updated MacOS.

https://www.macworld.com/article/673697/what-version-of-macos-can-my-mac-run.html

If so, update and the problem is likely solved. If not, you might have to convince Apple to upgrade/fix the Mail app in 10.13.06 (High Sierra), unless someone else has a solution.

If compatible, simply upgrade the operating system and the problem is resolved with the newer built-in Mail app.

In my case I had to first clean out enough junk files to leave me with enough storage to download the new operating system.

With 10.13.6 (High Sierra) or older I don't have a solution.

Succeeded by upgrading my 2015 MacBook Air operating system from 10.13.06, to 10.15.7 (Catalina). Once I discovered that it was compatible, I had to clean up useless filed to gain enough storage for the new

You need to change the way you authenticate on Google. For this:

• go on your Google Account -> Security -> 2-factor authentication -> Application passwords
• create a password for Mail on your Mac
• on your Mac, in the Internet Accounts settings , remove the Google account that is failing (i.e. the one that shows with a Google icon)
• create a new account that is not using the Google conduit (last option in the list which reads something like "Create another account"), enter your Google email address and the application password created in the previous step
• you're set!

after a crash of ssd , In high Sierra , google didn't accept me to use my long passwords

a bypass is to generate application password , 16 bytes long (generated by google)

this bypass was not easy to find , it is an emergency solution (without upgrading OS)

a few days after I upgraded to Mojave , and I put new long passwords(choosed by me) , leaving application passwords

MAIL application in high Sierra is not compatible with OAUTH2 (and long passwords)

MAIL application in Mojave is compatible with OAUTH2 (and long passwords)

i was worry to upgrade , by having other troubles

Webmail seems to be the only solution right now for Google Mail, unless Apple is willing to upgrade OS Mail for High Sierra 10.13.6. iCloud Mail does work, which may allow for a solution if you want to change from Google Mail or forward to iCloud.

Doesn't matter. The mail.app might work (haven't tested. Using Thunderbird). But Google won't hook up to the Calendar.app, regardless. So, I've stopped using Calendar.app and using the calendar in Thunderbird instead, which is perfectly OK with Google Calendar, Google Mail, etc.

"My iMac is an old 2009 version, using High Sierra, 10.13.6"

That's your problem. I just got dinged with this, myself. Looks like we'll have to move into the 2020's and upgrade the OS. Which for this machine, means getting a new machine. Apple quit supporting these machines with 10.13.

Have an Mac Pro with High Sierra. Connecting the Mac Calendar with Google Calendar worked fine. Last week I started using a new disk with a new installation of the same OS and got the same problem. No way to make Google Calendar accept login.

Simple solution and, in a way better than using the Mac's Calendar: I have used Mozilla Thunderbird (free) as mail client since the ice age. Now I started using its calendar and connected it to Google Calendar in a minute.

Try Thunderbird...

https://www.thunderbird.net/en-US/

https://support.mozilla.org/en-US/kb/installing-thunderbird-on-mac

Great answer! I added an App Password separate from my gmail password and it worked great. Running macOS High Sierra (10.13.6) on an imac 2012. Thanks!

10.13.6 won't solve this problem. I have 10.13.6 and I can't send to gmail addresses. Apple quit supporting 10.13 years ago. I bit the bullet and bought a this-decade Mac.

Very simple and easy to understand... superb.. ive got an old mac running high sierra 10-13-6 changed password on google accounts had above problem.. followed your instructions to the letter and BAM!!!! straight in back up and running.. cant see what all these other peoples problems are..... just copy and paste the newly created 1 time password generated in the App Password section at bottom of page in your google accounts.. Security..2 step verication.. App Password...name the app ie Gmail and click create...copy n paste the password and follow your steps creating new account in apple mail using create new other account..simple..well done sir...

You don't use that password in Mail, but in a Browser at google or gMail, forget exactly where...it nit your Mail Password nut a separate password.