chew85 below recommended Polymail, which looks like it will hopefully become the best solution to replace Mailbox.
In the meantime, thanks for the tip about turning off bundling as I've switched to Inbox for the interim.
I just ran into this app that looks promising, polymail, while digging through the dropbox forum of people complaining about the shutdown. Looks like it will actually be a mailbox replacement if all pans out. Alpha seems to have just come out for mac, and iOS app soon according to the dev's twitter. I'm glad to finally have hope again.
I could never stand Inbox, was figuring I'd have to get used to Spark which seemed like the next best thing.
Another poster suggested PolyMail which is in beta and has all of those except an iOS version which is in the works. I would also add lists as an essential for me though I don't know if you can automatically send certain email to a list yet, granted I haven't looked too deeply into that functionality yet.