> Google Inbox used be called Sparrow (https://en.wikipedia.org/wiki/Sparrow_(email_client)), which was a regular app that Google acquired. I used it since the beginning. It was a new paradigm back in 2011, which is now the standard in modern clients.

Could you name a few apps that have the Inbox/Sparrow features like snoozing an email until some time in the future?

I would love to have that, I looked for Thunderbird plugin for that but failed to find one.