This is a messaging application with a Android application front end. User messages text, audio, photo, video are stored on the application server repository. The messages are stored in a datacenter within the USA and messages are deleted as soon as they are received by all users in a conversation. They messages are also deleted if it hasn't been retrieved within a day. So there is no need to fear about data being stored.
This app can use your email address for Sign-in process from third party Authentication services such as Google and Apple.