STU48 Mail is an official mail application for fans of STU48, where fans can receive emails from their favorite members. This app is available on Android and is free to download. The app allows users to register their favorite members and receive unique and personalized emails from them.

However, it should be noted that this app has a monthly subscription for users who want to receive emails regularly. The monthly subscription fee is 400 yen per member (tax included) for one month, starting from the date of application. The payment will be automatically charged to the user's Google Play account. If users want to unsubscribe from the monthly subscription, they can do so by accessing the "Subscriptions" section of their Google Play account at least 24 hours before the update date. It is important to read and understand the terms of use and privacy policy before using this app.

Overall, STU48 Mail is a great application for fans of the STU48 group who want to receive personalized emails from their favorite members. However, users should be aware of the monthly subscription fee and how to manage their subscription if they decide to use the app regularly.