When configuring your Gmail account in Outlook (or other mail clients such as Thunderbird and Mail apps on (older) smartphones), you might run into continues 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 will fail even when you supply the correct password.
Solution 1: Re-enable Basic Authentication
To solve this, you must 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”.
By default, Basic Authentication has been turned off in Gmail.
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.
When you use this solution, you can create a special “App Password” which you’ll then 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.
Secure your Gmail account with 2-Step Verification.
Native OAuth 2.0 support in Outlook
Native support for OAuth 2.0 in Outlook (2016/2019/365) is being worked on but nothing has been announced yet.