Email can be useful, but more often than not we’re deluged with useless messages from mailing lists we subscribed to – but subsequently forget to unsubscribe from. Now Google is reminding you with an unsubscribe prompt for unread emails.
The card appears at the top of your feed in both the Android app and Web interface, letting you know when you haven’t looked at an email from a sender for a while – in this case any emails from them in the last month. There’s a simple ‘Unsubscribe’ button or a No Thanks button to let you clear the card (and the subscription).
The card apparently started rolling out a week ago, so you should be starting to see it in your app and on the desktop now. It’s pretty handy, so see what email you can get rid of.