A few weeks ago, some users noticed that email clients such as Outlook, Thunderbird, etc. prompted for a Google password when using the @gmail account. When they re-enter their Google password, it gets rejected saying it’s incorrect.
Google began restricting its email service and how it could connect with third-party email clients, eventually phasing out “less secure apps.” It allows you to log into your email client with your primary Google email address and password, thereby weakening the overall security of your Google Account.
You can still use Google on a third-party app, but the app must support “OAuth2” (an authentication method that opens a dialog that allows you to log in to Google and allow the app to access your Google account) authentication), or you must use an application-specific password.
Most applications don’t know how to handle two factors. Therefore, you cannot enter an authentication code, so an application-specific password is created. This allows you to create a special password on a per-application basis. Once created, instead of giving applications like Outlook your Google password, you provide them with an “application-specific” password.