Messenger IM integrated with Dropbox API. You can share photos, voices, video, files with your friends using Dropbox.
But you have to sign in your Dropbox first. And then Messenger IM makes its own folder inside your Dropbox.
So if you share files, Messenger IM will upload the files to your Dropbox and will send links to the files to your friends.
It means Messenger IM does not collect your information. So you don’t have to worry about privacy.