German security researcher Mike Kuketz has tested mail apps for Android. He found out that the apps Blue Mail and Type-App send the user's login data including the email passwords to the manufacturer's sites. Although both apps are said to have different developers, Kuketz found that the POST requests in both apps are nearly identical. This suggests that the same people are behind both apps. Bottom line: If you were or still are using one of those apps you should assume that your accounts are compromised. Consequently, you should alter your mail passwords as soon as possible! Kuketz recommends trustworthy open-source mail apps like K-9.