MailDigest

The mail summariser you can hand a phishing mail to.

MailDigest reads a mirror mailbox that you forward your mail to, summarises every message with a language model, has a second, independent instance check it for phishing, and sends you the result as plain text on Telegram, Discord or Signal. You see what is going on in your inbox without opening your inbox — and without anything clickable ever reaching you.

Real mailbox ──forwarding──► Mirror mailbox ──► MailDigest ──► Messenger

The security model in five sentences

1. MailDigest never gets access to your real mailbox, only to a dedicated mirror mailbox — and it deletes nothing there.
2. Before a language model sees anything, deterministic code reduces the mail to plain text: no HTML, no MIME parts, no attachment binaries.
3. The language models have no tools, no network access and no file access — the only thing they can produce is text in a validated JSON field.
4. What reaches you has been checked by code one last time: no clickable links, no attachments, no markup — domains appear defanged as example[.]com.
5. If anything goes wrong, you get a note ("This mail could not be processed safely — no content delivered.") instead of unchecked content — nothing disappears silently.

The path a mail takes — each stage only sees what the previous one let through:

[1] Ingest        code   IMAP read-only, seen flag, dedupe
[2] Sanitizer     code   MIME → plain text; HTML, links and attachments stripped
[3] Summarizer    LLM    no tools, no network, no files; JSON output only
[4] Critic        LLM    second instance with its own prompt: phishing check
[5] Output check  code   no links, no markup, domains defanged
[6] Messenger            Telegram, Discord or Signal

The two LLM stages are the only ones that interpret foreign text — and the only ones that can do nothing. Deterministic code stands in front of them and behind them. Details: docs/SECURITY.md.

Installation

You need Python 3.11 or newer (a small VPS or a Raspberry Pi is enough), a second, empty IMAP mailbox as the mirror, and a Telegram bot, a Discord webhook or a running signal-cli. A language model is optional.

Debian 13+, Kali and Ubuntu 26.04+ — with apt. MailDigest has its own signed package repository, so installation and updates run through the tool you already use:

curl -fsSL https://kpafi.github.io/maildigest/apt/maildigest-archive-keyring.gpg \
  | sudo tee /usr/share/keyrings/maildigest-archive-keyring.gpg > /dev/null
echo "deb [signed-by=/usr/share/keyrings/maildigest-archive-keyring.gpg] https://kpafi.github.io/maildigest/apt stable main" \
  | sudo tee /etc/apt/sources.list.d/maildigest.list
sudo apt update && sudo apt install maildigest

Fedora 43+ — with dnf, from a COPR project:

sudo dnf copr enable kpafi/maildigest
sudo dnf install maildigest

Everywhere else — with pipx:

pipx install maildigest

pipx install --force --editable .

python3 -m venv .venv && source .venv/bin/activate && pip install -e .

mkdir -p ~/.local/share/man/man1 && cp man/maildigest.1 ~/.local/share/man/man1/

Quickstart

maildigest init                # create the configuration (file gets mode 0600)
maildigest connect-mail        # mirror mailbox: test access, choose folder
maildigest connect-llm         # OPTIONAL: connect a language model (free ones too)
maildigest connect-messenger   # Telegram/Discord/Signal, test message
maildigest test                # end-to-end self-test with a sample mail
maildigest instructions --edit # what matters to you (changeable at any time)
maildigest run                 # continuous operation (Ctrl-C exits cleanly)

Every command asks for what it needs and explains the next step; maildigest --help shows the flow, maildigest <command> --help the options. At the end, connect-mail prints the instructions for setting up forwarding with Gmail, Posteo, mailbox.org or any other provider.

Secrets go either in at the prompt (they then live in config.toml, mode 0600) or through environment variables, in which case the file holds nothing:

export MAILDIGEST_IMAP_PASSWORD=…
export MAILDIGEST_LLM_API_KEY=…
export MAILDIGEST_TELEGRAM_TOKEN=…

For cron instead of continuous operation: maildigest run --once. Running it as a service: docs/OPERATIONS.md.

What a message looks like

📧 Heating meter reading on Thursday
From: Meier Property Management (meier-property[.]example) · 12.03. 09:14
The property management announces a reading of the radiators. Access required between 9 am and 1 pm.

The frame of the message (From:, 📎 Not processed:, 🔍 Notes: …) is always English; the summary itself is written in the language from [general] language. The line 🔍 Notes: … only appears when there is something to report — a failed sender check, a punycode domain, hidden text in HTML. Stripped links appear in place as [Link #1: example[.]com].

Unimportant mail does not arrive one by one but collected once a day:

🗂 12 low-priority mails: 8 newsletter, 3 notification, 1 other

And when something smells wrong:

⚠️ SUSPECTED PHISHING: sender domain does not match the claimed sender, reply address differs
📧 Urgent payment request [important]
From: Boss (mail-security[.]example) · 12.03. 03:41
Alleged payment request from the boss, transfer to be made today.
🔍 Notes: reply address differs from the sender

The mirror mailbox

MailDigest never reads your real mailbox. It reads a second, empty mailbox that you forward your mail to — pure storage that you never read yourself, ideally with a different provider than your main mailbox and with its own single-purpose password. What matters is that IMAP can be used with a password; maildigest connect-mail knows which providers can and tells you the matching instructions when you enter a host or mail address.

Hosting it yourself — not yet in a release; on main only. If you run MailDigest on a server of your own, maildigest selfhost-mail --domain mirror.example.org writes the Postfix and Dovecot configuration, the DNS records, an apply script and a checklist; you run the privileged steps yourself with sudo, and --check --wait-for-mail then proves the whole chain down to a real forwarded mail arriving. It needs a domain of your own and port 25 reachable from the internet, which rules out nearly every home connection. Step by step: docs/OPERATIONS.md §6. If that sounds like more than you want to own, the €1/month providers in the table are the better answer.

With or without a language model

MailDigest runs without any language model out of the box: after maildigest init, [llm] provider = "none" is set — no account, no credit card, no API key. In this mode you get subject, sender, a labelled excerpt of the mail text and of every readable attachment, the list of blocked attachments — and all warnings. Phishing protection does not depend on the model: failed SPF/DKIM checks, diverging reply addresses, punycode domains, hidden text in HTML and stripped links are all computed in code. What a model adds is real summaries instead of excerpts, an importance rating (and with it a meaningful collected digest), and the critic that checks the summary against the mail text.

maildigest connect-llm presents the options as a list to pick from:

Triggering it from your phone (optional)

While maildigest run is running, it reacts to exactly two words from your chat:

Anything else — including "summarise yesterday's mail for me" — is discarded without being read, answered or passed to the language model. That is deliberate: arbitrary text into a language model whose answer then drives actions is exactly the coupling this tool avoids. With run --once under cron the commands are served at the end of the next run.

Whoever can write into that chat can trigger fetches and thus cause cost at the model provider. With a private bot chat that is only you; if chat_id is a group, turn it off with accept_commands = false under [messenger.telegram]. The alternative without any back channel is a systemd timer or cron.

Customising

In config.toml:

[general]
deliver_min_importance = "normal"   # low = everything individually, high = urgent only
low_digest_time = "18:00"           # when the collected digest arrives

[summarizer]
instructions = "Invoices and appointments are always important. Advertising never is."

The instructions steer style, focus and importance. They cannot switch off the security rules — the critic never even sees them. You do not have to edit the file for this:

maildigest instructions                                                    # show
maildigest instructions --add "Anything from my university is important."  # append a line
maildigest instructions --edit                                             # edit in your editor
maildigest instructions --set "Only invoices and appointments count."      # replace entirely
maildigest instructions --clear                                            # delete

Up to 2000 characters, multiple lines allowed; takes effect from the next run.

FAQ

Why do I not get links? Because the link is the weapon. Phishing works by getting you to click, and in a messenger clicking is especially easy. MailDigest replaces every link with [Link #1: example[.]com] and breaks all the dots so your messenger does not linkify any of it. If you want the full (defanged) addresses appended as a list, set [links] footnote = true.

Why is my .docx invoice not summarised? Because MailDigest only opens what it can open safely: plain text files and PDFs, and those only if the first bytes match the declared type and extraction runs through in a sandboxed subprocess. Office files can execute macros, archives smuggle content past filters, .html attachments are an attack path of their own. All of those show up as a line "📎 Not processed: invoice[.]docx (34 KB)" — so you know it is there and decide yourself.

What about phishing as an image? That is the best-known gap: no OCR, no image analysis. A screenshot with text yields a summary like "mail without text with one image attachment" — conspicuous, but not protection. Encrypted mail (PGP/S-MIME) is likewise not decrypted; the message says so.

Can the AI be taken over by a mail? It cannot take over anything, because it is allowed nothing: no tool, no network, no file. A successful prompt injection can at most produce a wrong summary — against which a second instance checks with its own prompt and with facts computed in code, and the suspicion shows up as a note line in your message. The note "mail contained instructions to the AI (ignored)" does not hang on the model alone either: forged program markers, masses of invisible characters and literal instructions to a language model are detected in code before any model is asked.

Where is my data? The mail text only exists in memory while the mail is being processed. The SQLite file holds state and metadata, plus two short-lived exceptions of already checked, defanged text: the lines for the collected digest and a delivery not yet confirmed. The logs contain no mail content unless you set log_level = "DEBUG". The sanitised mail text goes to the language model — choose your provider accordingly or use a local model.

Why does a mail arrive twice? Because in case of doubt MailDigest would rather deliver twice than lose something: the state "checked" is stored before sending. If the process crashes exactly in between, the same message can arrive a second time.

Every mail comes back as "could not be processed safely"? Most likely a max_tokens limit that is too small. Many current models are reasoning models and subtract their thinking tokens from the response budget; with a small limit the JSON gets truncated and MailDigest fails closed. Out of the box there is no limit — only set one if you deliberately want to cap the cost per call, then 4096 is safe for classic models.

Why is no API key included? Because this program is open source. A bundled key would be scraped and revoked within days, and the bill would go to someone else. Without signing up anywhere it works without a model; whoever wants summaries connects their own, free options included.

What happens in the mirror mailbox? Unread mail gets read, marked as seen and, if you set move_processed_to, moved into that folder (your server needs the MOVE extension; otherwise the mail stays put as read with a note in the log). Nothing is ever deleted; there is no code path for it — not even an EXPUNGE.

Limitations of this version

The places where you should not rely on MailDigest:

• Barely any field experience. Version 0.2.0 ran against real counterparts for the first time in September 2026: one mirror mailbox at web.de, one model via OpenRouter, one Telegram bot — one environment, one user, a few days. Everything else is tested against mocks (2000+ tests, an attack corpus, two documented test rounds with black-box testers). Expect surprises on the first run and start with maildigest test --dry-run.
• Open findings are listed with severity and fix direction in docs/TESTING.md §7 — among them a mail made of millions of empty MIME parts that extends a fetch cycle by about half a minute.
• Image phishing remains open, see the FAQ. Encrypted mail is not read; you still get header, sender and the note line, and go into the real mailbox for the rest.
• Signal only as a note to self. The adapter writes into "Note to Self" and requires a running signal-cli --daemon.
• New warning heuristics are uncalibrated: the detection of AI instructions, the threshold for "HTML part differs from text part" and the rule for when several forgery signals add up to a phishing warning are tuned against test mail, not against your inbox. Too many warnings are more likely than too few.
• Moving can only fail in production. connect-mail does not check whether your server supports MOVE and whether the target folder exists; nothing is lost, the mail stays put as read.
• One mailbox, one process, no dialogue. No multi-mailbox operation, no access to your real mailbox, no chat with the bot beyond /digest and /status.

Two deliberate quirks that can look like bugs: delivered text carries no formatting (bullets become •, headings and italics disappear — formatting in a sender's name is a trust signal, and MailDigest leaves that to no one), and for mail with both a text and an HTML version, MailDigest summarises the text version while your mail program shows you the HTML one. If the two differ noticeably, that appears as a note.

Documentation

In short: the README explains the tool, docs/ explains the program.

The documents marked German are historical records of how the project was built and decided; they are kept in their original language.

Licence and status

Version 0.2.1 (see CHANGELOG.md): the first public program, 0.2.0, now installable and updatable through apt and dnf. Still little field experience and an honest list of open points, above and in docs/TESTING.md §7. Bugs and findings go in as a GitHub issue (the bug-report form has the right fields), security problems privately, see CONTRIBUTING.md.

Licence: MIT, see LICENSE.