Google may block sign-in attempts from some apps or devices that do not use modern security standards. Since these apps and devices are easier to break into, blocking them helps keep your account safe.
Some examples of apps that do not support the latest security standards include:
- The Mail app on your iPhone or iPad with iOS 6 or below
- The Mail app on your Windows phone preceding the 8.1 release
- Some Desktop mail clients like Microsoft Outlook and Mozilla Thunderbird
Step-by-step guide if you want to allow less secure apps:
- Login to your App State Gmail account.
- Click on the Google Apps logo in the top right corner of your browser.
- Click on Manage your Google account.
- At the top of the page, click the Security tab.
- Scroll down to Less Secure App Access and click the Off link arrow.
- On the next page, click the grey tab next to Allow less secure apps: OFF, to turn access on (the tab will be blue and checked when on).
Authentication in Outlook, Thunderbird, and other apps will now work.