I like the idea but https://inbox.google.com already solved this for me.
Occasionally I'll set two reminders because I forgot I already set one, but overall I'm doing more and replying to things at the right time without much effort, so it's been a successful switch for me.
Still, it is tricky for such an app to get stickiness from all kind of users.
After a few weeks of usage one thing that bothered me was that Inbox was slower. I continued to use it until I found that I had missed a few mails because Inbox had classified them incorrectly. I figured I'd rather use Gmail and make sure I didn't miss any mail, even if I have to sift through a few more mails. It basically comes down to what you prefer to tolerate type 1 or type 2 errors. And, search has always been good.
By default the columns are 'To Do', 'Doing' and 'Done' but this is just an example and can be changed. The idea of Drag is to be a universal way to manage your emails. Whether that's a To Do list or simply a better way to categorize your emails.
Some of our internal team are simply creating multiple lists so they're visually available (to be dealt with) in a more intuitive way than Inbox or traditional Gmail.
Love to hear your thoughts. Always good to get feedback from users of like-minded products/features.