When configuring your Gmail account in Outlook (or other mail clients such as Thunderbird and Mail apps on (older) smartphones), you may run into continuous password prompts or sync errors.
This is because Google has turned off Basic Authentication by default for all new accounts and accounts which haven’t synced within the last 30 days and only lets you authenticate via the OAuth 2.0 standard.
As a result, you’ll get Send/Receive errors (0x800CCC0E) and could get prompted for your Gmail password again in Outlook and the login could fail even when you supply the correct password.
Solution 1: Re-enable Basic Authentication
A quick way to solve this, is to re-enable Basic Authentication for Outlook in your Google Account Settings. This can be done via the “Allow less secure apps” page where you set it to “On”.
Solution 2: Enable 2-Step Verification (Recommended)
Another way to go would be to enable “2-Step Verification”. This is a bit more work but also quite a bit more secure and highly recommended.
Outlook for Office 365, Outlook 2019 and Outlook 2016
When using Outlook for Office 365, Outlook 2019 or Outlook 2016 (except for the Volume License msi-version), Outlook will prompt you for your credentials and the additional verification step as these versions offer native support for OAuth 2.0 for Gmail accounts.
Previous Outlook versions
When you are using Outlook 2016 (Volume License msi-version), Outlook 2013 or previous, then you can create a special “App password” which you’ll have to use within Outlook to logon to Gmail rather than using your regular password.
For step-by-step instructions to set this up see: Outlook and 2-Step Verification for Gmail accounts.