Zero metadata, group descriptions, native audio/video calls and much more! - Delta Chat

Zero metadata, group descriptions, native audio/video calls and much more!

March 31, 2026 by Delta Chat and chatmail core release teams

With the latest 2.48+ releases,<br>a chat message reveals close to zero metadata to servers.<br>For cryptographers and messenger enthusiasts, here are the key points on how we turned email very close to zero-metadata:

No cleartext Auto-Submitted or threading headers.<br>In addition to Subject, To, and group membership headers, we’re now also protecting<br>Auto-Submitted, References, and In-Reply-To.<br>This means that all meaningful header metadata now lives exclusively in the encrypted part of messages,<br>implementing full Header Protection (RFC 9788).<br>Transport servers only see a minimal so-called outer envelope.

Randomized Date header.<br>The outer Date is 5-day randomized, preventing timestamp-correlation<br>from attackers with access to temporary server message archives.<br>Delta Chat would not need this header at all,<br>but we decided to maintain compatibility with other encrypting email apps,<br>and classic email servers,<br>which often require this outer Date header to function at all.

SecureJoin v3 hides cryptographic identities.<br>When the user scans a QR code or clicks on an invite link,<br>multiple administrative messages are exchanged<br>in order to establish a chat and verify the encryption setup.<br>The new SecureJoin protocol (link contains more beautiful hand drawings!)<br>encrypts all initial messages,<br>and also shows<br>how to skilfully evolve a protocol to be both forward- and backward-compatible,<br>thus avoiding any friction for users.

No cryptographic key information in OpenPGP messages anymore.<br>We have finally enabled OpenPGP anonymous recipients<br>after waiting five months to give everyone time to upgrade their chatmail clients first.<br>Please make sure all your devices, and those of your contacts, are using at least<br>the v2 security-upgrade releases from August 2025 .<br>Especially apps older than June 2025 might encounter “unable to decrypt” messages otherwise.

No “Sealed Sender” yet, but also no phone numbers or private data<br>recorded at chatmail relays.<br>Chatmail profiles are created with random addresses<br>and without asking for any personal information.<br>We have some ideas about eventually implementing “Sealed Sender”,<br>but are more likely to aim for Autocrypt2 support first,<br>a new IETF specification draft for Post-Quantum-Cryptography and Reliable Deletion (“Forward Secrecy”).

orange: random, green: hidden, everything else: no meaningful data

Native calls on Android and iOS!

Audio and video calls on Android, iOS<br>now behave like native phone calls:<br>you can keep a call running in the background<br>while switching to a different chat or even another app.<br>Another useful use case is to talk while playing in-chat games like chess!<br>Under the hood, calls use peer-to-peer WebRTC<br>with signaling via regular Delta Chat messages.<br>The feature is still behind the “debug calls” setting but probably not in the next release anymore.

Native video calls on DeltaTouch (Ubuntu Touch)

Google and Apple are highly problematic centralized authorities for the mobile ecosystem,<br>which is why we are supporting developments on alternative mobile ecosystems<br>to the best of our abilities and resources.<br>Luckily, there are some private donors supporting development of DeltaTouch in particular,<br>a pretty much feature-parity Delta Chat client available on many “Lomiri” platforms.<br>DeltaTouch recently also landed audio/video calls, compatible with Delta Chat and all other chatmail clients .<br>If you have C++ and QT knowledge and interests,<br>by all means consider helping in the Codeberg DeltaTouch repository,<br>and the friendly and skillful developers behind it.

Group and channel descriptions

Groups and broadcast channels now support descriptions<br>that members see in the group profile.<br>Descriptions are end-to-end encrypted and synced with member additions,<br>making it easy to tell new members what a group is about.

Background audio message player

For those of us who like interacting via audio messages, this is golden:<br>both Desktop and Android now support playing audio messages in the background.

Download on demand revamped (what a journey!)

We had to fundamentally re-implement the years-old “download on demand” feature,<br>because it was relying on “cleartext headers” that aren’t available anymore (see the intro on zero-metadata above).<br>For larger messages, and messages with an attachment,<br>Delta is now internally sending two messages, one small and one large.<br>This provides receivers the choice to first download all small messages,<br>and automatically or optionally download the larger ones:

Calls can get through without first downloading potentially megabytes of attachments.

Delta Chat iOS notifications work without crashing on large messages.

Not yet fully downloaded messages are correctly placed in chats (instead of weird 1:1 email messages).

We still...