Orchestra, the Palo Alto-based maker of Mailbox, a popular iPhone email app, was bought by Dropbox for as much as $100 million.

The 13-person company sold for an unknown amount of money to Dropbox, which offers cloud-based storage, but estimates range from "well above $50 million" to "around $100 million," according to TechCrunch.

Orchestra, which has 1.3 million people on reservation for its app, cited its desire for rapid growth as a factor in the sale.

"The product (Mailbox) needs to grow fast, and we believe joining Dropbox is the best way to make that happen," the company's website states.

The app has been in the Apple App Store for only a month. It currently processes 60 million emails per day, according to its website.

Orchestra was founded in 2011 and has received $5 million in Series A funding in November 2011 from Charles River Ventures, SV Angel, Kapor Capital and CrunchFund, according to the company's Crunchbase profile.

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