While it started out as a service focused on storing and syncing files, Dropbox has branched out into many other directions in the past few years. However, some of those non-core experiments are coming to an end soon. The company has unveiled plans to shut down two of its mobile apps, namely Mailbox and Carousel. The former is an email client that went live on iOS in 2013, a month after which Dropbox acquired it. One year later, an Android version was released, along with Carousel, an app dedicated to viewing all the photos you have in your Dropbox account right next to the ones on your phone. It also uploaded all the shots you took on your handset to Dropbox. However, Dropbox found that most people still viewed images inside its main app, which can also handle automatic in-the-background image uploads by itself. So it doesn't make a lot of sense for Carousel to exist as a standalone offering, which is why it will be shut down on March 31, 2016. Oh, and certain "key features" from Carousel will make it to the main Dropbox app in the future, apparently. Mailbox will cease to operate on February 26. There's a FAQ already up that deals with making the transition to a new email client as easy as it can be. Source 1 Source 2 Source...
Source: http://www.gsmarena.com/dropbox_announces_plans_to_shut_down_mailbox_and_carousel_next_year-news-15384.php