OS X 10.10.3 adds Support for Google 2-Step Verification
When logging in with Google in the Mail app on OS X, you you may have gotten an error message. That is because you have 2-step verification enabled on your account. You have to go into your account and create an app-specific password, allowing you to log in. The mail app didn’t know that you have 2 passwords to enter, giving you an error message. Now, with OS X 10.10.3 it will load Google’s website to log in and then you can enter in your 2-step verification code. This allows you to just use the 6 digit code and not have to create an app-specific password.