Google deprecated their OAuth1.0 implementation some time ago and we've finally updated our service to use the newer OAuth2.0. This is good news because the new interface offers a better sign in experience with better mobile rendering. And it has better support from Google.
Most of our customers are already using the new OAuth2.0 user experience because we've made it the default for any accounts that don't use their own custom Gmail credentials.
If you are using a custom credentials for Gmail, you'll have to request a OAuth2.0 client ID in your Google Developer account and then add the ID and secret to a new CloudSponge Gmail Consumer Credential and assign it to your domain or as the default for your account. We have updated our documentation to describe the new process.