Engadget reports that Gmail's "Inbox by Gmail" web interface and Android app are proactively offering up a suggestion to unsubscribe from any promotional emails that haven't been opened in the past month.
This could be significant. Most good senders focusing on engagement are looking at six, twelve, or eighteen month engagement windows when considering who's still likely to want to receive their email messages, but Google is suggesting a much smaller window.
So many unanswered questions here. Will unsubscribes increase? We will see. And how many folks out there use "Inbox by Gmail" and will other email user interfaces follow suit?
Here's more on this from the XDA Developers blog.