Dropbox is thinking outside of the, well, box.

The cloud file sharing and storage company just snapped up tech start-up Orchestra, the company behind the email app Mailbox. Mailbox, which just went live last month, is a free iPhone app that promises to simplify email for users. The company says it now delivers more than 60 million emails a month.

"To be clear, Mailbox is not going away," Dropbox said in a statement. "The product needs to grow fast, and we believe that joining Dropbox is the best way to make that happen."

Dropbox did not disclose financial details of the acquisition. The Wall Street Journal reported that Orchestra had raised $5.4 million in funding in 2011.

The purchase may mean big things for Dropbox. Since launching in 2008, Dropbox has swelled in size and value — it was worth an estimated $4 billion at its last financing, and now serves more than 100 million users.

Tomio Geron at Forbes says the purchase could suggest "broader ambitions" for Dropbox, which has set out to distinguish itself from cloud storage rivals by adding a slew of new features.

My guess is that Dropbox will eventually build (or buy) a number of features or applications on top of all the data and content that people are storing within the service. That could include the ability to use or manage photos, documents, music, movies or even address books. That’s one way for Dropbox to start charging for different services beyond just additional storage space. It’s also a way to keep users attached to its service and not drifting away to others like Google Drive or Apple iCloud.

This is not to say that Dropbox will necessarily build its own email service to rival Gmail. But Mailbox sits on top of Gmail and helps people manage their files that they receive in email to save within Dropbox. In addition, if one of Dropbox’s key uses is sharing files to collaborate with others, then connecting those files over email is a natural fit. Expect to see more of these types of acquisitions or applications launching from Dropbox. [Forbes]