Nathan Ingraham, Engadget:
It's not a huge surprise -- neither product has received any meaningful updates since their announcement, and the photo-sharing space in particular is hotly contested right now. Still, these were splashy new products that seemed like it might help give Dropbox an identity beyond the file sharing and syncing it is known so well for.
Mailbox was purchased by Dropbox back in 2013 for $100 million, but after the announcement of an Android app and a forthcoming Mac app in 2014, development seemed to stop entirely on the product. It's a shame, because it really was a novel and useful email app that deserved more resources than it seems it got.
I held out hope for Mailbox, even though the iOS app hasn't received any meaningful updates for awhile, and the Mac beta has been buggy and languishing. This announcement was inevitable, but that doesn't quite mitigate the feeling of dissapointment. I loved Mailbox. It's syncing and ease of use was unmatched, and I don't know of another client out there that will come remotely close to providing a similar experience.