Newton Mail is shutting down on September 25th, marking the formal end of the subscription-based premium email app.

Newton is the latest third-party email app casualty. It joins the ranks of gone-but-not-forgotten (by me, at least) apps like Sparrow and Mailbox as yet another victim of the fact that it’s really hard to come up with a viable business model for email apps.

As founder Rohit Nadhani explained in a Medium post, the company “explored various business models but couldn’t successfully figure out profitability & growth over the long term.” He cited the competition of free apps from Apple, Google, and Microsoft as too much to overcome.

Newton Mail — which began as CloudMagic — was originally a free service before it transitioned to a paid, subscription-based model in 2016. The service offered apps for Mac, iOS, Android, and Windows (a rarity for third-party email apps) along with a variety of clever features like automatic inbox organization.

With the impending shutdown, Newton is disabling new signups, and it won’t renew monthly subscriptions going forward. The company is also working with the App Store and Play Store to issue partial refunds on annual subscriptions that will obviously no longer be valid come September.