TutaBridge

A local IMAP/SMTP bridge for Tuta encrypted email. It runs a local IMAP+SMTP server that ordinary mail clients (Thunderbird, Apple Mail, mutt, …) connect to, while talking to Tuta's API and handling the end-to-end encryption transparently.

Available as a CLI and a desktop GUI (Tauri).

⚠️ Unofficial & unsigned. TutaBridge is an independent project — not affiliated with, endorsed by, or supported by Tuta. It logs into your account and decrypts your mail locally, outside Tuta's official apps; use it at your own risk. The released binaries are not code-signed, so macOS and Windows warn on first launch — see Install for how to get past that.

Features

• IMAP + SMTP servers on localhost (TLS), so any standard mail client works.
• Realtime sync over Tuta's WebSocket event bus — new mail, reads, moves and deletes show up without polling. A heartbeat + idle-timeout detect dead sockets and reconnect automatically.
• Attachments both ways — incoming mail is served as multipart/mixed; attachments composed in your client are uploaded to Tuta on send.
• Drafts, custom / nested folders, move, trash, and read/unread flags.
• 2FA (TOTP) login.
• Encrypted local cache — metadata in SQLCipher, bodies as individually encrypted .eml.enc files. Subsequent launches load from cache and only fetch the delta, so the client is usable immediately.
• Complete mailbox backup to portable .eml files (see below).
• Full mailbox + search — the whole account is listed over IMAP and searchable by subject, sender, date and (full-text) body from your mail client.

Install

Download the latest build from the Releases page. Every platform ships two flavours:

• a desktop app — a normal double-click GUI, recommended for most people;
• a CLI binary — a single executable you run from a terminal, for headless / server use.

Platform	Desktop app	CLI binary
macOS (Apple Silicon)	TutaBridge_*_universal.dmg	tutabridge-macos-arm64
Windows (x64)	TutaBridge_*_x64-setup.exe (or .msi)	tutabridge-windows-x86_64.exe
Linux (x64)	*.AppImage / *.deb / *.rpm	tutabridge-linux-x86_64

Because the binaries aren't signed, each OS needs a one-time nudge to run them:

macOS

Open the .dmg and drag TutaBridge to Applications. On first launch macOS says the app "cannot be opened because the developer cannot be verified" — right-click the app → Open → Open, which whitelists it permanently. (Plain double-click won't offer the override.)

Windows

Run the .exe / .msi. SmartScreen shows "Windows protected your PC" — click More info → Run anyway.

Linux

chmod +x TutaBridge_*_amd64.AppImage && ./TutaBridge_*_amd64.AppImage
# or:  sudo dpkg -i TutaBridge_*_amd64.deb     (Debian/Ubuntu)
# or:  sudo rpm -i  TutaBridge-*.x86_64.rpm     (Fedora/RHEL)

CLI binary (any OS)

The CLI files have no extension, so double-clicking does nothing useful (your OS may even open them in a text editor). Run them from a terminal:

chmod +x tutabridge-macos-arm64                          # make it executable
xattr -d com.apple.quarantine tutabridge-macos-arm64     # macOS only: clear Gatekeeper
./tutabridge-macos-arm64                                  # run

Getting started

1. Launch the app (or run the CLI). On first run it asks for your Tuta email, then your password and TOTP code if there's no saved session. The session is stored in your OS keychain, so later launches resume automatically.

2. TutaBridge shows the local connection details. Note the bridge password — this is generated by TutaBridge for local IMAP/SMTP auth and is not your Tuta password. (CLI: it's printed in the logs; GUI: it's on the main screen.)

3. Add the account in your mail client with these settings:

   	Server	Port	Security	Auth
   IMAP (incoming)	127.0.0.1	1143	SSL/TLS	normal password
   SMTP (outgoing)	127.0.0.1	1025	SSL/TLS	normal password

   • Username: your Tuta email
   • Password: the bridge password from step 2
   • Accept the self-signed certificate when the client prompts.

Keep TutaBridge running while you use your mail client — it's the local server the client talks to.

Client-specific notes

• Thunderbird: add the account manually (don't let auto-config probe public servers). Set both servers to 127.0.0.1 with SSL/TLS + "Normal password", and accept the certificate exception on first connect.
• Apple Mail: add an "Other Mail Account", then in Server Settings turn off "Automatically manage connection settings" so you can pin host 127.0.0.1, the ports above, and TLS.

Notes & limitations

• Search runs in your mail client and is honest: subject / sender / date search covers the whole mailbox; body (full-text) search covers messages whose body has been downloaded. Keep "every message body offline" enabled (or raise the offline-bodies limit) for full-mailbox body search.
• Self-signed cert is expected — the bridge only listens on 127.0.0.1, so traffic never leaves your machine.

Architecture

Syncer-driven, store-backed:

Tuta API  ←──  Syncer (background)  ──→  MailStore (in-memory)  ←──  IMAP server  ──→  mail client
                                                                ←──  GUI (stats)

• The syncer pulls from the Tuta API and populates an in-memory MailStore, backed by the on-disk encrypted cache.
• The IMAP server only ever reads from the store — it never makes API calls for reads.
• The only IMAP→network calls are mutations: mark read/unread (STORE \Seen) and trash (EXPUNGE). Sending goes through SMTP → Tuta's DraftService + SendDraftService.

The storage encryption key is derived from your Tuta session, so there's no extra password to manage; the cache is encrypted at rest.

Build from source

Requires the Rust toolchain and the tuta-repo submodule (git clone --recursive, or git submodule update --init --recursive).

cargo build                      # CLI + core
cargo build -p tutabridge-core   # core library only
cargo run                        # run the CLI from source
./dev.sh                         # GUI in dev mode (cargo tauri dev)

Files & locations

Config and cache live under your platform's app-data directory — on macOS ~/Library/Application Support/tutabridge/:

config.toml          account + ports + bridge_password + sync_limit
store.db             SQLCipher metadata + full-text body index
mails/<id>.eml.enc   per-mail encrypted bodies

sync_limit controls how many recent message bodies are kept offline; the full mailbox is always listed and metadata-searchable regardless. Set it to 0 (or tick "keep every message body offline" in the GUI) to download everything.

Backup

Export every email to a folder of plain .eml files — one file per message, in a directory tree mirroring your IMAP folders. This is a complete backup: it enumerates all mail from the server, not just the messages currently synced, so nothing is silently left out.

<output>/
├── INBOX/
│   ├── 20260528-144935_OtjDuDU--3-9.eml
│   └── …
├── Sent/
├── Trash/
└── Café/Projets/…

CLI:

tutabridge backup ~/TutaBackup

GUI: the Backup tab — pick a folder, watch the per-folder progress, done. (The bridge must be running; the backup reuses its signed-in session.)

Notes:

• Format: .eml (RFC 2822). Opens natively in Thunderbird / Apple Mail / Outlook, survives Windows filesystems, and one corrupt file never takes down the whole archive. Filenames are date-prefixed so a listing sorts chronologically.
• Resumable / incremental: re-running into the same folder skips messages already on disk, so an interrupted backup resumes and a periodic re-backup only fetches new mail.
• Speed: messages already in the local cache export instantly; the rest are fetched from the server with a small politeness delay, so a first full backup of a large mailbox can take several minutes. Subsequent runs are fast.
• Scope: every folder, including Trash and Spam. Labels aren't separate folders, so a labelled mail is backed up once, in its real folder.

Testing

cargo test --workspace        # unit + integration tests

python3 scripts/test_imap.py  # integration test against a running bridge

The IMAP integration test connects to the local server and verifies TLS, auth, folder list, mail count, body fetch and search. It reads the bridge password from config.toml automatically.

SDK

TutaBridge depends on a few additions to Tuta's Rust SDK, vendored as the tuta-repo submodule. Each change is kept as its own single-commit branch off upstream for easy review / upstreaming — see SDK_PRS.md for the status of each.

License

GPL-3.0-or-later. TutaBridge links Tuta's Rust SDK (part of the GPLv3-licensed tutanota project), so it is distributed under the same license.