Delta Chat: encrypted messaging over email, without a phone number or account
Delta Chat uses email infrastructure as its transport layer. No central servers, no phone number — and with a Chatmail server, no email address required either.
Delta Chat: encrypted messaging over email, without a phone number or account
Delta Chat doesn’t set up a new server. It’s a messaging app that uses email as its transport layer — and with it, the decentralized email network that has existed for decades.
That might sound like a workaround, but it has a concrete consequence: there’s no central operator to subpoena, no platform that can suddenly disappear or get acquired, and no phone number required. The network is email itself.
How it works
Delta Chat sends messages as encrypted emails via standard IMAP/SMTP. Your contact receives them as email, but sees a chat interface — not a traditional inbox. The email server doesn’t know messages are being exchanged: it only sees encrypted packets.
For end users, Delta Chat feels like a normal messaging app. Under the hood, everything runs over email infrastructure.
No email address required: Chatmail
The most privacy-friendly way to use Delta Chat is via a Chatmail server — a specially configured email server for Delta Chat.
When registering on a Chatmail server, a random email address is automatically generated for you. You provide no name, phone number, or existing email address. The address is a meaningless string tied to nothing.
Chatmail servers automatically delete messages after 7 days and accounts after 90 days of inactivity. They enforce mandatory end-to-end encryption for all messages.
You can also use an existing email address — at your own provider, Proton Mail, or a self-hosted server. That gives more control but requires an existing email account.
Encryption
Delta Chat uses OpenPGP as the encryption standard, with Autocrypt for automatic key exchange. Keys are exchanged on the first message — no key servers, no manual import.
SecureJoin — making contact via QR code — provides guaranteed end-to-end encryption that protects against active network attackers. Groups created with verified contacts never degrade to unencrypted communication.
Since Delta Chat version 2 (July 2025), all communication is end-to-end encrypted by default. The app makes this transparent to the user — no lock icons, no warnings, it just works.
Perfect Forward Secrecy (PFS) is not yet present. OpenPGP doesn’t natively support it. If a private key is ever compromised, previously intercepted messages are theoretically readable. Autocrypt version 2 (planned for 2026) will introduce automatic key rotation — the closest approximation of PFS within the OpenPGP framework.
What the email server sees
This is the most honest limitation of Delta Chat: email protocol exposes sender and recipient addresses in headers. The server sees:
- Which address sent to which address
- Date and time
- The subject line (Delta Chat sets this to ”…” — useless to an observer)
The server does not see:
- Message content (end-to-end encrypted)
- Group composition (stored locally, encrypted)
- Your contact list
With a Chatmail server, the addresses are randomly generated — they link to nothing. With a regular email provider, they’re tied to your account.
Delta Chat is not the right choice for anyone requiring maximum metadata protection. For anyone wanting to protect content without depending on central servers, it’s a strong option.
Security audits
Delta Chat has been independently audited multiple times:
- Cure53 (2023): 7 vulnerabilities found, 5 security-relevant. Primarily affecting the desktop application.
- ETH Zurich (March 2024): 20 issues found in the SecureJoin protocol, all resolved in version 1.44.
- Radically Open Security (December 2024): Two CVEs found in the underlying rPGP library (CVE-2024-53856, CVE-2024-53857: crash on malformed input and resource exhaustion). Both patched and deployed immediately.
The pattern is consistent: issues are found and fixed. No known exploits in the wild.
Installing and getting started
Android: via Google Play, F-Droid (recommended on GrapheneOS), or Huawei AppGallery.
iOS: via the App Store.
Desktop: Linux (Flatpak, Arch, Nix), macOS, Windows — download from delta.chat.
On first launch:
- Choose “Chatmail server” for anonymous registration without an email address
- Or enter an existing email address
- Share your QR code or invitation link to connect
Multiple profiles per device are supported — useful for compartmentalization.
Honest caveats
No PFS yet — see above. Autocrypt v2 in 2026 will partially address this.
Metadata visible to email server — unavoidable due to email protocol. With Chatmail the addresses are random; with regular email they’re not.
Group size — Delta Chat is not designed for groups above 150 members.
Sync speed — outgoing messages sync to additional devices roughly twice per hour, not in real time.
Disappearing messages — if the recipient uses a regular email client rather than Delta Chat, they can copy messages before they disappear.
Who Delta Chat is for
Direct value:
- People who don’t want to give a phone number and don’t want to create a new account
- Anyone skeptical of central platforms who prefers existing decentralized infrastructure
- Organizations that run their own email server and want data sovereignty
- Users who want to separate multiple digital identities via multiple profiles
- Anyone who already trusts email as a channel and wants an encrypted chat layer on top
Less suitable for:
- Anyone requiring maximum metadata protection (Session, SimpleX, or Briar are better for this)
- Anyone who requires PFS today
- Large groups (above 150)
- Anyone prioritizing voice or video calls
Delta Chat vs. the rest
| Delta Chat | Signal | Session | SimpleX | |
|---|---|---|---|---|
| Phone number required | No | Yes | No | No |
| Central server | No (email infrastructure) | Yes (US) | No (decentralized) | No (relay queues) |
| Perfect Forward Secrecy | No (2026 via Autocrypt v2) | Yes | Yes | Yes |
| Metadata protection | Limited (email headers) | Good | Excellent | Excellent |
| Cost | Free | Free | Free | Free |
| Works without internet | No | No | No | No |
| Open source | Yes | Yes | Yes | Yes |
Background
Delta Chat was developed by Merlinux GmbH in Freiburg, Germany — a small, independent organization with no venture capital. The project has existed since 2017 and is funded through public grants and donations. The source code is fully open source (GPL-3.0).
See also:
- SimpleX Chat guide — no identifier, maximum anonymity
- Session guide — decentralized, onion routing
- Threema guide — paid, Swiss, no phone number
- Briar guide — P2P via Tor, works without internet
- Signal and Molly review — Signal with extra privacy options