ICD360S Mail

Secure, end-to-end encrypted email for desktop and mobile

Your emails are encrypted so only you and your recipient can read them.

---

Important

Your emails are never stored on your device. They are fetched live over mutually authenticated TLS and displayed in memory only. No forensic artifact remains after the app closes.

---

How It Works

graph LR
    A["Your Device"] -->|"mTLS + E2EE"| B["mail.icd360s.de"]
    B -->|"PGP Encrypted"| C["Recipient"]
    B -->|"DANE + DNSSEC"| D["DNS"]
    style A fill:#1565C0,stroke:#0D47A1,color:#fff
    style B fill:#2E7D32,stroke:#1B5E20,color:#fff
    style C fill:#1565C0,stroke:#0D47A1,color:#fff
    style D fill:#4527A0,stroke:#311B92,color:#fff

Loading

👁️ What the server sees Sender address Recipient address Subject line Date and time Message size

🔒 What's encrypted (E2EE) Message body Attachments Attachment names & types Inner MIME structure Everything inside the payload

---

Features

🔒 Encryption OpenPGP E2EE — PGP/MIME (RFC 3156) Native Go engine — 27 MB in < 1 sec TOFU key pinning — warns on key change Zero-access storage — admin can't read mail WKD — auto key discovery for Thunderbird/ProtonMail Autocrypt — key exchange in every email Password-protected mail — AES-256-GCM for external recipients	🛡️ Authentication Mutual TLS — per-user client certificates Device approval — admin-controlled enrollment Remote revocation — instant wipe on revoke PIN unlock — randomized keypad layout DANE + DNSSEC — verified transport ARC signing — auth preserved on forward
🙈 Privacy RAM-only cache — zero disk, wiped on lock Self-hosted DoH — no Google, no Cloudflare Header stripping — IP/hostname removed from outgoing PII-safe logging — auto-redaction of sensitive data No telemetry — zero analytics, zero tracking	📊 Security Monitoring 10 health checks every 30 minutes SPF, DKIM, DMARC, MTA-STS, TLS-RPT CAA, DNSSEC, DANE (TLSA) IPv4/IPv6 blacklist (43 providers) Recipient security in compose — E2EE / DANE / TLS / Plaintext

---

Cryptography

Note

All cryptographic operations use modern, audited standards. No legacy algorithms.

Component	Standard
🔑 Signing	Ed25519 (EdDSA)
🔐 Encryption	X25519 / ECDH (Curve25519)
✉️ Messages	OpenPGP (RFC 9580, PGP/MIME RFC 3156)
🏦 Vault	AES-256-GCM + Argon2id (64 MiB / 3 iters / 4 threads)
📡 Transport	Mutual TLS + DANE (TLSA 3 1 1) + DNSSEC
🔍 Key discovery	WKD + Autocrypt Level 1

---

Download

Tip

All downloads are served over HTTPS with cryptographically signed version verification.

Desktop

Linux packages: DEB, RPM, tar.gz, Flatpak repo

Format	Download
DEB (Ubuntu/Debian)	icd360s-mail.deb
RPM (Fedora/RHEL)	icd360s-mail.rpm
tar.gz	icd360s-mail-linux.tar.gz

Flatpak (recommended for Fedora Silverblue/Kinoite + auto-updates):

flatpak remote-add --if-not-exists icd360s \
  https://mail.icd360s.de/downloads/mail/flatpak/icd360s.flatpakrepo
flatpak install icd360s de.icd360s.mailclient

Updates land via flatpak update (or automatically through GNOME Software / KDE Discover). The single-file .flatpak bundle is still published per-release but the repo install avoids the "Update Issue" warning that bundle-only installs cause.

Mobile

Android flavors: F-Droid, Samsung, Huawei, Google Play

Flavor	ARM64	ARMv7	x86_64
Universal	Download	Download	Download
F-Droid	Download	Download	Download
Samsung	Download	Download	Download
Huawei	Download	Download	Download
Google Play	Download	Download	Download

---

Building from Source

git clone https://github.com/ICD360S-e-V/mail.git
cd mail && flutter pub get
flutter run -d macos    # or: windows, linux

Platform requirements

Platform	Requirements
All	Flutter 3.41+, Dart 3.6+
Android	Java 17, Android SDK
iOS/macOS	Xcode 15+
Linux	libgtk-3-dev, libsecret-1-dev, libjsoncpp-dev
Windows	Visual Studio 2022 with C++ workload

---

About ICD360S e.V.

ICD360S e.V. is a registered German nonprofit (eingetragener Verein). Every active member receives a free, secure @icd360s.de email account with E2E encryption and cross-platform access.

Caution

The live service at mail.icd360s.de is available exclusively to members. This repository contains the open-source code — the operational service is private.

---

📜 Security Policy · ♿ Accessibility · 🤝 Contributing · 📄 License

ICD360S e.V. · Amtsgericht Memmingen, VR 201335

kontakt@icd360s.de · Impressum · Datenschutz