Forgetting to update a recently changed Gmail password in Outlook is not the only reason Microsoft Outlook may reject your Gmail password. Since July 15, 2014, Google has blocked access to Gmail accounts through apps and email clients that use the Basic Authentication protocol, such as Outlook. To get the program to accept your Gmail password, activate your Google account's Basic Authentication option or use Google's Two-Step Verification and App Passwords features.
Enable The Basic Authentication Feature
Browse to the Google Less Secure Apps page, sign in to your Google account and then click the Turn On radio button. Outlook is now able to access your Gmail account. If prompted, click the OK button on Outlook's pop-up Internet Email box to authenticate your Gmail account with the program.
Activating the Less Secure Apps option leaves your Gmail account more vulnerable to attack.
Though the Less Secure Apps option is necessary for the desktop version of Outlook, many mobile apps support the most recent security standards. For example, use the Mail app on an iOS device running iOS 7 or above, the Gmail app for iOS and Android or even mobile version of Outlook itself for iOS or Android.
Set Up Two-Step Verification
Browse to the Two-step Verification Start Setup page, sign in to your Google account and then click the Start Setup button.
Enter your mobile number in the Phone Number field. Select the Text Message (SMS) radio button to receive a numeric verification code by text message. If you would prefer an automated voice call, select the Voice Call radio button.
Enter the verification code you received in the Enter Verification Code field and then click Next to open the Trust This Computer page.
Select the Trust This Computer check box and then click Next.
Only select the Trust This Computer option if you trust the people who have access to your computer. An unauthorized person can access your Gmail account without a code if your computer is trusted.
Click the Confirm button to activate the feature. Your Two-Step Verification Account page automatically opens after you activate the feature.
Create An App-Specific Password
Click the App-Specific Passwords tab. If your Two-Step Verification Account page does not automatically open, manually browse to the tab.
Click the Manage Application-Specific Passwords button and, when prompted, re-enter your Google Account password.
Click the first drop-down box, select Other(Custom Name) from the list of options and then enter Outlook in the open field. Click the Generate button to create the password.
Record the password that was generated.
Go to Outlook's Change Account dialog window. This window is found under Account Settings in the File tab. Select your Gmail address from the list of accounts and click Change. Enter the system-generated password in the login information and check the box next to Remember Password.