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mm_mailman

A Mattermost bot that relays messages to multiple channels via a guided two-step broadcast wizard. Users interact with the bot exclusively via direct messages.

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Architecture

The bot is built on mmbot_framework, a shared library that handles the WebSocket lifecycle, session management, middleware, and command routing. postbot adds only the broadcast-relay logic on top.

postbot/
  main.py        # Entry point: load config, build bot, run
  bot.py         # PostBot(BaseBot) — all command handlers and broadcast wizard
  config.py      # PostBotConfig(BotConfig) — env var loading and validation
  database.py    # SQLite broadcast log
  patches.py     # SSL workaround
  channels.json  # Channel group definitions (visible groups, private groups, whitelist)

Message flow:

Mattermost WebSocket event
  → IgnoreSelfMiddleware     (drop own messages)
  → DMOnlyMiddleware         (drop non-DM messages)
  → CommandDispatcher        (route to handler by trigger prefix)
  → handler / broadcast wizard (PostBot.on_message)

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Configuration

Create a .env file in the postbot/ directory:

# Required
URL=mattermost.yourdomain.com
TOKEN=your_bot_access_token
TEAM_NAME=your-team-name

# Optional — shown with their defaults
SESSION_TTL_SECONDS=300
SESSION_CLEANUP_INTERVAL_SECONDS=60

# Logging
LOG_LEVEL=INFO                  # File log level
CONSOLE_LOG_LEVEL=WARNING   # Console (stdout) log level — set to INFO to see startup messages
LOG_FILE=logs/bot.log

# Postbot-specific
BOT_LOG_CHANNEL_ID=             # Channel ID for broadcast audit messages (empty = disabled)
CHANNELS_JSON_PATH=channels.json
DB_PATH=broadcast_log.db

Tip: Set CONSOLE_LOGGING_LEVEL=INFO to see WebSocket connection and startup messages in the terminal.

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channels.json

Defines the channel groups the bot can broadcast to. Loaded at startup and extendable at runtime via !add_group / !add_private_group.

{
  "groups": {
    "Group Name": ["channel_id_1", "channel_id_2"]
  },
  "private_groups": {
    "Private Group Name": ["channel_id_1"]
  },
  "whitelist": ["channel_id_allowed_for_cherry_pick"]
}

• groups — visible to all users via !get_groups
• private_groups — visible only via !get_private_groups
• whitelist — channel IDs that may be targeted individually by name or ID, outside of groups

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Installation

Local / Dev

Requires Python 3.14+ and uv.

cd postbot
uv sync
# create and fill in .env (see Configuration section above)
uv run main.py

Running Tests

cd postbot
uv run pytest -v

Container (Podman / Docker)

cd postbot
podman build -f Containerfile -t mailman-bot .
podman run --env-file .env -v ./channels.json:/app/channels.json:ro mailman-bot

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Bot Commands

All interaction happens via direct message to the bot. Messages in channels or group chats are ignored.

Command	Description
!help / help / --help / man	Show usage instructions
!channels	List all channels the bot has access to in the current team
!id <channel name>	Look up a channel's ID by name
!get_groups	List all visible channel groups
!get_private_groups	List all private channel groups
!add_group <JSON>	Add one or more public groups at runtime
!add_private_group <JSON>	Add one or more private groups at runtime
(any other message)	Start the broadcast wizard

Broadcast Wizard

Sending any message that isn't a command starts a two-step broadcast:

1. Target selection — the bot asks which channels or groups to send to. Accepted formats:

   • Group names (from !get_groups / !get_private_groups)
   • Individual channel names (must be on the whitelist)
   • Channel IDs directly
   • Comma-separated combinations: Group A, Group B, some-channel-name

2. Confirmation — the bot shows a preview of recipients. Reply yes to send, no to cancel.

Files attached to your original message are relayed alongside the text.

Sessions expire after SESSION_TTL_SECONDS (default 5 minutes). If your session expires before you confirm, the bot sends a DM notification.

Adding Groups at Runtime

!add_group {"New Group Name": ["channel_id_1", "channel_id_2"]}

Multiple groups in one command:

!add_group {"Floor 1": ["id_a", "id_b"], "Floor 2": ["id_c", "id_d"]}

Changes are persisted to channels.json immediately.

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Broadcast Log

Every successful broadcast is recorded in a SQLite database (broadcast_log.db by default), including sender, timestamp, target channels, and message content.

If BOT_LOG_CHANNEL_ID is set, a summary is also posted to that channel after each broadcast.