I think this is obviously not just a talent acquisition. An email client is something that Dropbox needs in the long run to provide awesome integrated experience for your productivity tasks. Without it, they won't be able to compete with Google on user experience.

I'm really happy for this acquisition. It could be an early sign of a new trend in which companies heading to IPO buy strategic products and teams in the early stages to build something awesome together.

Facebook's Instagram acquisition could be seen this way, but it was much more defensive move. Mailbox acquisition is clearly done from more win-win perspective.