Email app Mailbox was sold for rumoured $100m

"Disrupt alumnus Dropbox made the second in a series of super-savvy, super-early stage acquisitions today, picking up hyped-up email management app Mailbox in an acquisition that we’re calling “DropMail.”
We had been hearing that Mailbox was raising money, piquing the interest of Andreessen Horowitz among others, which is why today’s news that the company sold to the harmoniously named Dropbox didn’t come as a surprise. Sometimes an acquisition is the easiest way to raise resources for growth — especially when you’re tackling as expensive a problem as email. And have a six-figure wait list.
And we’re hearing that this particular acquisition was not cheap — The post-pivot startup cost the storage company “well over” $50 million, according to multiple sources. And we’ve heard that that the price was around $100 million in cash and stock."

Source:  Techcrunch, 15th March 2013

Note - Mailbox only launched in January 2013