This could be related to 746705, but in any case, accounts using @gmail.com addresses will be blocked unless you go and turn on support for "less secure apps" in settings.  I'm guessing that the authentication method has been deemed insecure by Google.

That said, if you're using google to manage your own domain, geary works without any problems.

Here is the relevant text from the mail I got:
		
Hi Sriram,
Google just blocked someone from signing into your Google Account xrixxx.ramkxxxhna@gmail.com from an app that may put your account at risk.
Less secure app
Friday, June 30, 2017 1:49 PM (PT)
Aloha, OR, USA*

Are you the one who tried signing in?
Google will continue to block sign-in attempts from the app you're using because it has known security problems or is out of date. You can continue to use this app by allowing access to less secure apps, but this may leave your account vulnerable