Sterna Mail

Sterna Mail is open-source and built for JMAP, the new and faster internet standard for email, with full support for classic IMAP/SMTP too. Just your mail, on the server you choose.

Why JMAP?

Most email apps communicate with your server using an older protocol called IMAP. JMAP is its modern successor: it syncs faster, uses less battery and data, and was designed for today's mobile devices. Servers like Stalwart support JMAP, and Sterna is built to take full advantage of it.

Sterna also supports classic IMAP and SMTP, so it works with any standard mail provider. Choose the protocol when adding an account, or simply enter your email address and let autodiscovery find the server for you.

What Sterna stands for

- Privacy first. No tracking, no ads, no analytics, no Google services. Remote images and tracking pixels are blocked by default; tapped links can be stripped of tracking parameters and confirmed before opening. - Free and open source. Licensed under the GPLv3 — anyone can read, audit, and improve the code. - Modern and calm. A clean, fast Material 3 interface with its own brand identity that follows your phone's theme and language.

Features

Reading and organising

- Unified inbox across multiple accounts (JMAP and/or IMAP/SMTP), fully offline with local cache. Large folders page in as you scroll, fetching older mail from the server. - Conversation view — threads collapse into one row with a message count. - Nested folders shown as a collapsible tree; create, rename, delete, and manage subfolders. - Configurable swipe actions, flag/star, archive and delete with undo, multi-select bulk actions, snooze, report spam, empty trash (with undo), sort and unread-only filter. - Search-as-you-type (server-side and instant local results) with advanced filters (from, subject, has-attachment, date). - Calendar invites preview as an event card; one tap adds them to your calendar app (no calendar permission needed).

Writing and sending

- Compose with recipient chips, autocomplete, and email validation. Multiple identities each with its own signature, attachments, and drafts. - Undo send, schedule send (with a screen to view and cancel pending sends), and reminders for forgotten attachments or large recipient lists. - Opens mailto: links from any app or browser, prefilled with addresses, subject, body, and CC/BCC.

Accounts and setup

- Add an account with just email and password (/.well-known/jmap autodiscovery), password-free OAuth 2.0 sign-in (device flow), or manual IMAP/SMTP with provider presets. A test connection button is available before saving. - Per-account colour, sync window, and notification toggle. Encrypted credential storage (AndroidKeyStore) and app lock (biometric or PIN).

Encryption

- OpenPGP (via OpenKeychain): read and send signed and/or encrypted mail (PGP/MIME) on both JMAP and IMAP/SMTP. Decrypted content is never written to disk.

Notifications and server power

- Push for new mail with no Google or FCM (JMAP EventSource, IMAP IDLE or UnifiedPush), grouped per account, with quiet hours. - Server-side vacation responder and Sieve filter rules, mailbox quota display.

Polish

- Sterna's own Arctic (light) and Pelagic (dark) palette, optional Material You, adjustable message text size, settings export/import, screen-reader-friendly UI, and coastal empty-state illustrations.

Languages

Sterna's interface is fully translated into nine languages:

English, French, German, Spanish, Italian, Portuguese, Dutch, Russian, Polish.

It respects your system language out of the box, and you can override it per-app in Settings → Appearance.

License

GNU General Public License v3.0