Sterna Mail

A fast, private JMAP email client for Android, fluent in classic IMAP/SMTP too. No ads, no tracking, no Google.

A complete, daily-drivable email client: read, organise, search, write, schedule, and send mail (with attachments) over JMAP or IMAP/SMTP, across multiple accounts, fully offline-capable, with OpenPGP encryption, push notifications, and remote content blocked by default.

Features

Reading and organising

- Unified inbox across multiple accounts (JMAP and/or IMAP/SMTP), fully offline with a local cache - Conversation view with collapsed threads and message counts - Nested folders shown as a collapsible tree; create, rename, and delete subfolders - Configurable swipe actions, 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 with server-side and instant local results, plus advanced filters (from, recipient, subject, has-attachment, date) - Calendar invite preview as an event card with one-tap addition

Writing and sending

- Compose with recipient chips, autocomplete, email validation, multiple identities, attachments, and drafts - Undo send, schedule send, and reminders for missing attachments or large recipient lists - Opens mailto: links from any app, prefilled with addresses, subject, body, cc, and bcc

Accounts and setup

- Add an account with email and password using JMAP autodiscovery - Password-free OAuth 2.0 sign-in (device flow or authorization code with PKCE) - Manual IMAP/SMTP setup with provider presets and a test connection option - Per-account colour, sync window, and sync switch - Encrypted credential storage with AndroidKeyStore and app lock via biometric or PIN

Encryption

- OpenPGP via an external app such as OpenKeychain - Read and send signed and/or encrypted mail (PGP/MIME) on both JMAP and IMAP/SMTP - Decrypted content is never written to disk, with opened attachments stored in app cache until cleared

Notifications and server features

- Push for new mail with no Google or FCM: JMAP EventSource, IMAP IDLE, or UnifiedPush - Grouped per account, with quiet hours - Two home-screen widgets for unread count and recent mail - Server-side vacation responder and Sieve filter rules - Mailbox quota display

Appearance

- Sterna's own Arctic (light) and Pelagic (dark) palette, with optional Material You - Adjustable message text size, settings export and import - Screen-reader-friendly interface

Languages

Dutch, English, French, German, Italian, Polish, Portuguese, Russian, Simplified Chinese, Spanish

Respects the system language out of the box, and can be overridden per-app in Settings → Appearance.

Privacy

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.

Requirements

- Android 8.0 (API 26) or newer - A JMAP or IMAP/SMTP mail account

Disclaimer

Sterna Mail is an independent, open-source project. Its interface is freely inspired by K-9 Mail (now Thunderbird for Android). It is not affiliated with K-9, Thunderbird, or any third-party service. All trademarks belong to their respective owners.

License

GNU General Public License v3.0