Google has decided to not allow spam filtering apps, like Spamdrain, to access Gmail mailboxes any longer. This change will prevent us from protecting you from spam and marketing emails starting as soon as July 15 2019. We are deeply sorry for the inconvenience this will cause. We’ve done everything we can to resolve this, but Google has refused to cooperate.
Currently gmail based address can be used only in order to sign up but cannot be added to the filtering. This means that you can use gmail based email address for sign up, to enter it as a contact email address and use for billing purposes. However, we are denied to filter email address and stop the spam messages.
If you want more details about this change, please see this blog post:
Keywords: gmail, google, OAuth2