LibreMail

A free and open-source email client for Android, built with Kotlin, Jetpack Compose and Material 3 (Material You). LibreMail aims for a friendly default experience with power-user features tucked under an Advanced Settings group.

Status: in development. Material You shell; onboarding — a first-run flow from a welcome screen through a vendor picker (Outlook/Hotmail, Gmail, Yahoo, iCloud, or Other) and per-vendor setup to your first account's inbox; account setup — Outlook/Microsoft via OAuth 2.0 (AppAuth/PKCE), Gmail/Yahoo/iCloud via app password, and generic IMAP/SMTP, all with a live connection test and Keystore-encrypted credentials; IMAP receive — background sync (WorkManager) into a local Room cache with pull-to-refresh, backfilling your entire mail history (resumable) with an optional device-only retention cap; reading — message bodies fetched on open and rendered in a hardened WebView (JavaScript off, remote images blocked by default), with mark-read, star, and delete; composing — a rich-text HTML editor with a formatting toolbar and per-account signatures that sends multipart/alternative (HTML with a plaintext fallback) through a reliable background outbox (WorkManager-queued and retried, with a viewable outbox folder), plus device-contacts autocomplete, reply, and drafts; on-device new-mail notifications (no push service) with persisted settings; instant push via a foreground IMAP IDLE service; attachments — downloaded on demand and opened in a system viewer, and attach files when composing; multiple accounts — a unified inbox with per-account filtering; search across cached mail and the server (IMAP SEARCH); Outlook/Microsoft send via Microsoft Graph with an SMTP/XOAUTH2 fallback; an opt-in app lock (biometric/device-credential) that binds the encrypted cache key to your unlock; mailto: link handling with optional default-mail-app registration; and opt-in, F-Droid-safe debug reporting — local crash/error capture that you review (with a PII disclaimer) and submit only on an explicit action.

Features (target MVP)

• Send and receive email with Outlook/Microsoft (OAuth 2.0), Gmail, Yahoo and iCloud (app password), and any other IMAP/SMTP provider.
• Guided first-run onboarding: welcome → vendor picker → per-vendor setup → your inbox.
• Material You dynamic theming, light/dark, edge-to-edge.
• Rich-text compose with a formatting toolbar, per-account signatures, and phone/account contacts integration.
• Offline-first: a local Room cache with full-history backfill and an optional device-only retention limit.
• Modern, opt-in security: OAuth 2.0 (Authorization Code + PKCE) for Outlook, Keystore-encrypted credentials, optional SQLCipher cache encryption, and a biometric/device-credential app lock.

Tech stack

Area	Choice
Language / UI	Kotlin, Jetpack Compose, Material 3
Min / target SDK	33 (Android 13) / 37 (Android 17)
Build	Gradle 9.6, AGP 9.2, Kotlin 2.4.0 (KSP, no KAPT)
DI	Hilt
Local cache	Room (single source of truth) + DataStore
Async / sync	Coroutines + Flow, WorkManager
Email transport	Jakarta / Angus Mail (IMAP + SMTP, XOAUTH2)
OAuth	AppAuth-Android

Building

Prerequisites

• Android Studio (latest) or the command-line Android SDK.
• JDK 17–21 for the Gradle daemon. AGP 9.2 does not yet support JDK 25, so if your JAVA_HOME points at JDK 25, run Gradle with a 17–21 JDK (Android Studio's bundled JBR is fine; from the CLI, set JAVA_HOME to a JDK 21 install).
• Android SDK Platform 37 (platforms;android-37.0) and Build-Tools 37.

# Install the required SDK packages (accept licenses when prompted):
sdkmanager "platforms;android-37.0" "build-tools;37.0.0"

# Build, test and lint the debug variant:
./gradlew :app:assembleDebug
./gradlew :app:testDebugUnitTest
./gradlew :app:lintDebug

# Install on a connected device / emulator:
./gradlew :app:installDebug

local.properties (git-ignored) must point sdk.dir at your Android SDK; Android Studio creates it automatically.

Accounts and onboarding

On first launch LibreMail runs a short onboarding flow: a welcome screen, a vendor picker (Outlook/Hotmail, Gmail, Yahoo, iCloud, or Other), per-vendor setup, and an "add another account?" prompt before it drops you on your first account's inbox. You can add more accounts later from settings; a unified inbox merges them with per-account filtering.

LibreMail supports three kinds of account:

• Outlook / Hotmail — signs in with OAuth 2.0 through Microsoft (AppAuth); no password is stored. See Outlook / Microsoft account setup below.
• Gmail, Yahoo and iCloud — preconfigured IMAP/SMTP that authenticate with a provider app password (not your normal account password), preferring STARTTLS where the provider supports it. Onboarding links you to each vendor's app-password page. Gmail requires 2-Step Verification to be enabled before Google will issue an app password.
• Other — a manual IMAP/SMTP form (host, port, security, and credentials) for any other provider.

App passwords and OAuth tokens are held in a credential store encrypted with the Android Keystore, and every account runs a live connection test before it is saved.

Outlook / Microsoft account setup (OAuth client)

Outlook uses the Microsoft identity platform with OAuth 2.0 + PKCE (no client secret). Send goes through Microsoft Graph (sendMail, their preferred API) with SMTP/XOAUTH2 as a fallback; receive is IMAP. Graph and Exchange Online are separate resources, so one consent grants every scope and per-resource access tokens are minted from the one refresh token. A working client ID ships with the build; to use your own Azure app registration:

1. Azure portal → App registrations → New registration. Supported account types: Accounts in any organizational directory and personal Microsoft accounts.
2. Authentication → Add a platform → Mobile and desktop applications; add the redirect URI org.libremail.outlook://oauth2redirect and enable Allow public client flows.
3. API permissions (delegated): Microsoft Graph → Mail.Send (primary send), plus Office 365 Exchange Online → IMAP.AccessAsUser.All and SMTP.Send (receive + SMTP fallback). openid/email/offline_access come from OIDC.
4. Copy the Application (client) ID into secrets.properties as OUTLOOK_OAUTH_CLIENT_ID (it overrides the built-in default).

Privacy and data flow

LibreMail is offline-first: your mail lives in a local cache, and by default network traffic goes only to your mail providers (IMAP/SMTP, plus Microsoft's OAuth and Graph endpoints for Outlook). There is no analytics SDK and no always-on telemetry. The privacy-sensitive extras are all opt-in:

• Cache encryption — the Room cache can be encrypted at rest with SQLCipher. With the optional app lock (biometric or device credential) enabled, the cache key is bound to your authentication, so the database is only decrypted after you unlock the app.
• Debug reporting — off by default. When enabled, crashes and errors are captured locally; you review the full report — shown with a plain-language PII disclaimer — and it is sent only when you explicitly submit it, to a configurable (optional) endpoint. There is no hosted crash pipeline collecting reports in the background.
• Android Backup — off by default. When you turn it on, only safe app settings are backed up; the encrypted-database key, account credentials, and the mail cache are excluded. Because Android's backup transport can route data through Google, it stays disabled unless you opt in — the kind of optional behavior F-Droid lists as an anti-feature.

Architecture

Offline-first, unidirectional, layered:

ui/        Compose screens + ViewModels (MVVM), Navigation Compose, Material You theme
domain/    Models + repository interfaces
data/      Room (entities, DAOs, database) + repository implementation (source of truth)
di/        Hilt modules

The UI observes Room via Flow; a sync engine (Angus Mail over IMAP/SMTP, plus Microsoft Graph for Outlook send) writes into Room, and an auth layer (AppAuth for OAuth and an Android Keystore-backed credential store for app passwords) handles sign-in.

License

LibreMail is licensed under the GNU General Public License v3.0 — see LICENSE. SPDX identifier: GPL-3.0-or-later.