Companies that focus on e-mail marketing, such as Return Path, have been around for years. The company works with some 163 app developers and has more than 8,000 customer emails read for "training purposes". It's the same with Edison Software. The developers of the Edison Mail app have also encouraged employees to read the emails of users to improve the smart answer feature.
In addition, the companies also use automated scanning methods to browse the e-mails. Google itself has gone beyond this practice for privacy reasons last year. However, the search engine giant continues to allow this method to other developers. Other e-mail services such as Yahoo or Microsoft also allow this, but get the consent of the users before.
So far, no misuse of the information is known, but many users it may bring a bad feeling in the stomach, if employees of the company may have read the personal e-mails or continue to read along.
If you're one of them, you might want to upgrade to a first-party app like Gmail, Inbox on Gmail, or Apple's mail app.