If you wish to just get this over with without reading the entire instructions, just sign in to your Gmail on the internet because your password is correct, then click this link (click here) and change it to on instead of off. 
As of July 15, 2014, you might have problems connecting to Gmail via Outlook and other mail clients such as Thunderbird and Mail apps on (older) smartphones. This is because Google 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.
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 “Enable”.
Another way to go would be to enable “2-Step Verification”. In that case, you can create a special “App Password” which you’ll then use within Outlook to logon to Gmail rather than with your regular password. This is the more secure approach and highly recommended. For step-by-step instructions to set this up see: Outlook and 2-Step Verification for Gmail accounts.
Allow less secure apps to access accounts
We have added a feature that allows you to block sign in attempts at the domain or Organizational Unit level from some apps or devices that do not use modern security standards.
See the Frequently Asked Questions section below for examples of apps that do not support the latest security standards.
Since these apps and devices are easier to break into, blocking them helps keep your users’ accounts safer.
Default less secure apps account access
Existing users with any programmatic login requests with plain passwords in the last 90 days will be able to use less secure apps by default. New Google Apps users and existing Google Apps users with no programmatic login requests with plain passwords in the last 90 days will not. Instead, by default, they will see a “Password incorrect” error when trying to sign in to less secure apps. This is also what the user sees when the admin selects the Disable access to less secure apps for all users radio button.
Disabling access to less secure apps for all users
Use this setting when you want to ensure that access by a less secure app is unavailable to all.
- Sign in to the Google Admin console.
- Click Security > Basic settings.
Where is it? - Under Less secure apps, select Go to settings for less secure apps.
- In the subwindow, select the Disable access to less secure apps for all users radio button.
Once you’ve set Disable access to less secure apps for all users to on, affected users within the selected group or Organizational Unit will not be able to toggle access for less secure apps on or off themselves. You will have to set the setting back to Allow users to manage their access to less secure apps to allow them to toggle access for less secure apps on or off themselves.
Enabling less secure apps to access accounts
- Sign in to the Google Admin console. After sign in: I created a short cut so you don’t have to look for it forever.
- click here.
- Click Security > Basic settings.
Where is it? - Under Less secure apps, select Go to settings for less secure apps.
- In the subwindow, select the Allow users to manage their access to less secure apps radio button.
Once you’ve set Allow users to manage their access to less secure apps to on, affected users within the selected group or Organizational Unit will be able to toggle access for less secure apps on or off themselves.
