Penguin Mail is a mail and calendar app for Linux, written in Rust with GTK 4 and libadwaita. It's designed to be a lightweight, privacy-first alternative to Thunderbird or GNOME's built-in email.

What it does: • Aggregates Gmail, Microsoft (Outlook/Hotmail/Microsoft 365), Fastmail, iCloud, Yahoo, and any IMAP/POP3 account into one inbox • Calendar support for every account (Google Calendar, CalDAV) • Contacts with CardDAV integration • OpenPGP and S/MIME signing/encryption — keys never leave your machine • Gmail-style categories bar (Primary, Updates, Promotions, Social) • Send Later, Undo Send, templates, Markdown compose • A built-in AI assistant that can summarize threads, draft replies, manage rules, and search calendars. It runs on a local model (Ollama/LM Studio), an Anthropic API key, or Claude Code — you pick per job • Remote content blocked twice (WebKit filter + CSP), JS off by default • Runs in the tray at ~55 MB

It's GPL-3.0 and available as .deb, .rpm, Arch package, snap, tarball, and Flatpak. Not on Flathub yet — that's next.

We built it because existing Linux email clients felt bloated or didn't respect privacy. The AI assistant is a nice-to-have but not required — the app works great without it.

Feedback welcome: install experience, missing features, anything confusing. Happy to answer questions about the Rust/GTK4 architecture too.