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).

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).

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

cargo build                      # CLI + core
cargo build -p tutabridge-core   # core library only

GUI (Tauri + React) in dev mode:

./dev.sh                         # cargo tauri dev — opens the desktop app

Running the bridge

CLI:

cargo run            # or: ./target/debug/tutabridge

On first run it prompts for your Tuta email; the session is then stored in the OS keychain so later launches resume without a password (TOTP is prompted when required). The bridge prints the local connection details:

IMAP server: 127.0.0.1:1143 (SSL/TLS)
SMTP server: 127.0.0.1:1025 (SSL/TLS)
Username:    <your tuta email>
Password:    <bridge password — shown in the logs / GUI>

Point your mail client at those, accept the self-signed certificate, and use the bridge password (not your Tuta password) for IMAP/SMTP auth.

Config and cache live under ~/Library/Application Support/tutabridge/ (macOS):

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

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.