mailboxappHere’s a new bar for startups: Mailbox, the trendy iPhone email app, has been acquired even before clearing its wait-list of new users.

But what’s more interesting about this deal is the company making the acquisition — Dropbox — and what it could mean for Microsoft’s SkyDrive, Google Drive and other tech giants competing in the cloud storage business.

As reported by the Wall Street Journal, Dropbox is buying Orchestra Inc., the maker of Mailbox. It’s the first expansion beyond Dropbox’s core file storage and sharing business.

While deals like this are sometimes more about talent acquisitions, Dropbox says it will continue to operate Mailbox and also incorporate some of its technology into Dropbox itself. If this is the beginning of a trend for the company, it could make Dropbox a more well-rounded competitor in online services, competing head-to-head against its larger rivals.

The WSJ reports that Dropbox has been valued at $4 billion and has discussed the possibility of an IPO with investment bankers.

Orchestra, trying to manage significant demand for Mailbox, is using a clever countdown feature for people who download the app, showing their place in line and how many people have signed up after them. The iPhone app’s signature feature is the ability to quickly move messages out of the in-box and set them to reappear later, at a specified time.

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