WhatsApp is still the top dog among instant messaging apps. More than two billion people worldwide have it installed on their smartphones and billions of messages, images and videos are sent around the world every day. From a sustainability perspective, however, its popularity is controversial. WhatsApp collects, processes and sometimes even shares sensitive personal metadata. This, in addition to concerns about data protection, also negatively impacts the messaging platform’s energy balance and therefore its CO2 emissions.
Read more in this article: Open Source, Encrypted, Green(er): Secure Alternative Instant Messaging Apps to WhatsApp
While WhatsApp doesn’t disclose specific figures about its carbon emissions, one thing is clear: the more data an app collects, stores, and processes, the more energy it consumes. Every message, image, or voice note travels through networks and is stored in data centres—facilities that require significant electricity to operate.
With WhatsApp now integrating AI features into its messaging service, data traffic is expected to grow even further. And with it, so will the energy demand—and the CO₂ emissions. This trend is not unique to WhatsApp, but applies to all Meta platforms.
That’s why now is a great time to consider more sustainable alternatives. Luckily, they’re already out there. We’ve previously introduced Signal and Threema, two secure and privacy-focused messaging apps, and highlighted the benefits of open source technology.
But, there’s another free instant messaging platform worth highlighting: Delta Chat. It stands out for several reasons—it’s decentralised, uses minimal data and even lets you communicate with people outside the app.
Safe and decentralised
Delta Chat can actually do everything that other instant messengers can do. What makes it special is its technical structure. Unlike Signal and co, Delta Chat doesn’t send messages via its own servers, but instead uses the infrastructure of existing email addresses. Anyone with an email address can log into the app and send messages via a chat window. It doesn’t matter which email server is used.
This setup makes Delta Chat fully decentralised—offering users several key advantages. Unlike most messaging apps, which only allow communication within their own networks, Delta Chat lets you message anyone with an email address. If both users have the app, messages are automatically end-to-end encrypted and appear as standard chat messages. Only the first message is sent unencrypted, as it’s used to exchange the encryption keys. If the recipient doesn’t use Delta Chat, they receive the message as a regular email—and can reply directly from their inbox. That reply then appears as a chat message in the app.
That means the messages are secured while being transmitted, but could potentially be accessed on the mail server.
End-to-end encryption is only possible if both users are using Delta Chat or if the recipient’s email provider supports technologies like Autocrypt or PGP (Pretty Good Privacy). For example, email services like ProtonMail or Tutanota offer built-in end-to-end encryption.
Delta Chat is almost infinitely expandable
Delta Chat was launched in early 2019 by Merlinux GmbH, a company based in Freiburg, Germany. The project received funding from the European Union, including support from the Open Technology Fund. Since its launch, the app has been continuously developed by a global open source community. The source code is publicly available on GitHub, making the project fully transparent.
“Basically, our development is very community-driven,” explains Holger Krekel, who coordinates research and development for Delta Chat. “Many key features aren’t developed because of funding, but because friends of the project are interested and have the capacity to contribute.”
The app itself is intuitive to use and functions like a typical messenger. The only notable limitation is the lack of built-in audio and video calling. However, external tools—like the open-source platform Jitsi Meet—can be easily integrated. Thanks to its open design, Delta Chat can be expanded with a wide range of additional features, says Krekel.
As of April 2025, the app has been downloaded over 100,000 times from Google Play Store.
You choose how green it is
As Delta Chat is based on the infrastructure of email services and the end-to-end encrypted messages are only stored locally on the devices used; the app doesn’t need its own servers. This has the advantage that users remain independent of a central service provider that could arbitrarily change its terms of use and data handling. To ensure that this remains the case, a far-reaching innovation is planned for summer 2025 that will permanently prevent its centralisation.
By choosing the email provider through which Delta Chat is used, you can also influence the sustainability of your chat communication. If you use a provider whose servers run on green energy— such as Posteo—your communication within the app will do the same.
Delta Chat is also resource-efficient overall. “Basically, Chatmail Relay Servers are extremely energy-efficient compared to traditional email servers. They only store chat messages for transport until they are delivered to devices. This is usually no longer than 40 days,” says Holger Krekel. And, Delta Chat uses the “Chatmail Core” library. “This implements all network and server interactions in the Rust programming language, which runs very efficiently and resource-efficiently on all end devices.”
Sustainability: “Just a small, forgetful message forwarding machine”
Because Delta Chat does nothing more than encrypt and display messages directly on your device, it doesn’t generate any metadata. “It’s just a small, forgettable message forwarding machine that runs on efficient and tried-and-tested software,” says Holger Krekel. This makes the service both data- and energy-efficient.
As a result, running Delta Chat is also remarkably cost-effective. According to Krekel, around 100,000 users incur operational costs of only about €500 per year. The default server, nine.testrun.org, is powered entirely by green electricity.
Krekel also shared a useful tip for new users: “We always recommend getting a separate email address for chatting with Delta Chat, as mixing regular email communication with instant chat communication [can be] confusing.”
Interested in trying it out? Delta Chat is free to download and available on a wide range of platforms: Google Play Store, F-Droid, Huawei AppGallery (for Android), App Store (iOS), Mac App Store, Microsoft Store (Windows), and directly via the developer’s website for Android, Linux, Windows, and macOS. You can create a profile immediately—no existing email address required.
The post Decentralised, Efficient Without Being Addictive: Delta Chat Is Our Favourite Instant Messenger appeared first on Digital for Good | RESET.ORG.
