With the release of Mailbox for Mac also comes drafts, which has been sorely missing from Mailbox for iPhone and Android. But unlike most drafts implementations, which are handled by syncing messages to a drafts folder on an email server, Mailbox handles all your drafts on its own and stores them in Dropbox. This means that if you open another email client, your drafts won’t be there, but it also means that Mailbox can sync your drafts between desktop and iPhone as if they were instant messages.

"Drafts in IMAP are a terribly broken paradigm," says Beausoleil. "The Mac Mail app saves a new document in drafts every second, so you get an incredibly high-volume way of saving drafts that takes up space, makes search sluggish, and then every device has to sync all those things. It’s incredibly inefficient." I tested out the feature by typing an email reply into Mailbox for Mac. By the time I glanced over to my phone, the draft had already appeared in my message list.

Drafts is one more way that Mailbox for Mac feels most like a "messaging" client — the lifelong aspiration of Sparrow, with its bite-sized threaded messages and color-coded email recipients. With its swipe gestures for triaging messages, Mailbox sometimes even feels like a to-do app. The engine behind Mailbox, in fact, wasn’t originally even built for emails. Before Gentry Underwood and company built Mailbox they built Orchestra, a to-do app hosted in the cloud. "Mailbox was an iteration on Orchestra," says Beausoleil. "We didn’t know it was going to be email — but when when we did know [our system] became an abstraction of tasks and emails. You have things, and these things have sub-things. In the world of Mailbox it’s a thread that has emails, but it could also be a task that has notes."

So, you have to trust Mailbox to communicate all these abstracted changes back to your actual email provider (as you have with previous versions of Mailbox), but in my tests, it’s all gone down without a hitch. Since trying out the app several weeks ago, I’ve returned to Gmail on the web only to search for old items and contacts that Mailbox was taking too long to find. The beta app’s search is buggy, to say the least, although Mailbox says that search is still an area of intense focus for the final stages of the beta. Besides the occasional search, Mailbox has replaced the entire front-end interface for how I interact with email. With Mailbox on both desktop and mobile, it’s easy to forget that you’re dealing with IMAP email at all.

Even if Mailbox doesn’t ever add Exchange, it will have influenced the designers who work on Outlook

Yet, Mailbox is still very much only for a niche audience — people using Gmail and iCloud — in a world where so many businesses run on Exchange and require more advanced features. Only last week did Mailbox even add "print" and "report spam" functions to its app, at beta testers’ requests. And the app still doesn’t allow you to do things that have been possible for years in Google Apps and Outlook, like comparing calendars with a colleague to book meetings or flagging items for follow-up. Underwood admits, "There are some an intensely challenging tradeoffs between creating a simple, idealized workflow and supporting all the different ways people work."

It’s no stretch to imagine Dropbox acquiring an app like Sunrise to build out email-based scheduling, a common use-case. After all, to Dropbox, Mailbox is the means to an end, one piece of a larger puzzle. "What suite of tools would you want within an organization to get stuff done?" asks Underwood. "You can’t just answer it by where Mailbox is going, but [instead] by where Dropbox is going. We’re spending a fair number of design cycles on the next generation of Mailbox and Dropbox, and how those things fit together."

Mailbox still has plenty of work to do, even on the homefront. There are lots of bugs in the Mailbox for Mac beta, and there are still more email services to add like Exchange and Yahoo, which Underwood says his team is thinking about. But, much as Sparrow did before it, Mailbox is paving the way towards a future where email works faster, syncs instantly between all your devices, and just acts more like the other modern communication apps we use today. Even if Mailbox doesn’t ever add Exchange, it will have influenced the designers who work on Outlook, and on any email app henceforth. This might be Sparrow’s greatest legacy, that it challenged us to think of email in a different way. With its new Mac app, Mailbox has now picked up the torch.