maildirsink 0.1.0

SMTP でメールを受け取り Maildir / JSON に保存するだけの開発用メール受信ツール

maildirsink

A tiny tool that receives mail over SMTP and just saves it to a file. Like a development mail sink such as mailpit, but with no UI and no forwarding — it sticks to one job: receive and store.

日本語版は README-ja.md を参照してください。

Why

In the find-job project, notification mail was written directly into a Maildir by a shell script. maildirsink extracts just that "store mail locally" part into a general-purpose tool.

It commits to standard Maildir as the storage target, so it slots straight into Maildir-native MUAs (mutt / neomutt) and existing Maildir tooling (procmail, mbsync, and friends).

What it does

1. On startup, listens as an SMTP server on the given port.
2. On receiving a message, stores it in the given directory in the given format.
3. Nothing else — no forwarding, no web UI.

Storage formats

• maildir — standard Maildir. Incoming mail is written to tmp/ and then moved into new/ (the unread-mail spool). Filenames follow the standard uniqueness-guaranteeing scheme (time.Ppid.hostname). mutt / neomutt scan new/ directly, so no extra setup is needed.

• json — one JSON file per message:

  {
    "subject": "...",
    "from": "...",
    "to": "...",
    "date": "...",
    "message_id": "...",
    "body": "..."
  }
  

Note: Direct delivery to Thunderbird is intentionally out of scope. Thunderbird keeps a .msf summary cache and won't notice mail written into a Maildir from outside until you "Repair Folder". Maildir-native MUAs like mutt don't have this problem and pick up mail dropped into new/ immediately.

Install

pip install .
# or, for development:
pip install -e ".[dev]"

Usage

maildirsink [--port PORT] [--host HOST] [--format maildir|json] [--dir DIR]

Option	Meaning	Default
--port	SMTP listen port	1025
--host	Listen host	localhost
--format	Storage format (maildir / json)	maildir
--dir	Storage directory	./mail

Exposing on a LAN

The default localhost only accepts mail sent from the same host. To receive from another host (a container, a find-job instance on the LAN, etc.), listen on all interfaces:

maildirsink --host 0.0.0.0 --port 1025

Warning: There is no authentication and no TLS. Use it only within a trusted LAN. Do not expose it directly to the internet.

Reading mail (mutt / neomutt)

Just point your MUA at the Maildir that maildirsink writes to. Because there is no index cache like .msf, no repair step is ever needed.

set mbox_type = Maildir
set folder    = "/path/to/maildir"
set spoolfile = "+."
mailboxes     = "/path/to/maildir"

# Pick up mail that arrives while mutt is running
set mail_check = 5      # seconds
set timeout    = 10

Once mail lands in new/, mutt reflects it automatically.

Implementation notes

• Written in Python.
  • SMTP server: aiosmtpd (the stdlib smtpd was removed in Python 3.12).
  • Maildir writing: the stdlib mailbox.Maildir. Maildir.add() handles the tmp/ → new/ sequence and filename uniqueness for you (reference/maildir-delivery.sh is a hand-written example of the same).
• Character sets: MIME-encoded headers (=?UTF-8?B?...?=) are decoded.

Tests

pytest

License

MIT — see LICENSE.