DeadLetter
A no-bullshit email client.

Open-source, cross-platform email built in modern C++. Encryption first. Protocol agnostic. Extensible without compromise.

C++20 GPL-3.0 In Development
View on GitHub
Philosophy

Built on opinions.

Encryption is architecture, not a plugin.
OpenPGP and S/MIME live in the message pipeline. Every message passes through the crypto layer on the way in and on the way out. Not bolted on. Built in.
Your email lives on your machine.
Full local cache with offline-first sync. Compose drafts on a plane, search your entire history without an internet connection. Your data, your disk.
One client for all your accounts.
IMAP, Microsoft 365, Gmail, legacy Exchange — all behind a single interface. Unified inbox that actually unifies. No folder switching, no account hopping.
Extensions are real.
Stable C ABI plugin system with versioned APIs. Not fragile hooks that break every release. Write plugins that intercept, transform, and extend the entire message lifecycle.
Features

What you get.

PGP + S/MIME
Sign, encrypt, and verify with OpenPGP or S/MIME. Auto-encrypt when all recipients have public keys.
Unified Inbox
Virtual folder across all accounts. Unread-only toggle. Per-account color coding. One view, everything.
Tracker Blocking
Sandboxed HTML rendering. Remote content blocked by default. Tracking pixels stripped before display.
Full-Text Search
SQLite FTS5 index over every message. Search subjects, bodies, senders across all accounts. Instant, local, private.
Plugin System
Stable C ABI. Pre-send, post-receive, pre-render hooks. Toolbar and sidebar extensions. Permission-based security.
Offline First
Full local message cache. Differential sync with delta tokens. Queue operations offline, execute on reconnect.
Compatibility

One client. Every provider.

DeadLetter abstracts every email protocol behind a unified interface. Connect your personal Gmail, your work Office 365, your self-hosted IMAP server, and your company's legacy Exchange — all in the same window. Auto-discovery figures out the right protocol so you don't have to.

IMAP / SMTP Microsoft Graph Gmail API Exchange EWS
Cross-Platform

Native everywhere.

Windows
MSVC 2022
Linux
GCC 13+ / AppImage
macOS
Clang 17+ / .dmg
Status

In active development.

DeadLetter is being built in the open. The architecture is locked, the foundation is laid, and features are shipping phase by phase. It's not ready for daily use yet — but it will be.

Follow the project on GitHub to track progress, report issues, or contribute.