(Screen grab taken from DropBox's Web site)

Mailbox, the e-mail app that requires a reservation, announced Friday that it’s been acquired by the online file-storage service Dropbox.

The app, released last month, has earned high marks for its simple, intuitive design, which allows users to move quickly through cluttered inboxes. To keep the app from crashing due to high use, the company put a reservations system into place and saved people a spot in line when they downloaded the app. According to Mailbox, the app has is now delivering more than 60 million e-mails per day.

The new arrangement will allow the e-mail service to expand more quickly and let the Gmail-only service open its doors to other providers, the Mailbox team said in its post.

“To be clear, Mailbox is not going away. The product needs to grow fast, and we believe that joining Dropbox is the best way to make that happen,” the post read. It also hinted that future versions of Mailbox could integrate with features on Dropbox.

In a company blog post of its own, the Dropbox team said that they “fell in love” with Mailbox because it was simple and “beautifully engineered.”

The companies did not disclose how much the deal was worth. A report from the Wall Street Journal indicated that that Mailbox’s parent company Orchestra had received $5.3 million in funding in 2011.

Dropbox has been going through a lot of changes recently, making changes to its design and introducing new features that make the case that it can be used for a lot more than file-storage and sharing.

A new photo album feature, for example, shows that Dropbox has some ambition to focus on the lucrative online photo space. Another new feature, which allows users to preview documents stored on the site without having to download it.

The company has also made changes to its Mac desktop app, which includes a drop-down menu for at-a-glance access to the data stored online, as well as an easy way for users to share folders or files or easily see what other Dropbox users have sent their way.

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