SMTP2TG: smtp2tg

SMTP-to-Telegram gateway. Receives emails via SMTP and forwards them to Telegram chats.

Installation

From source

git clone https://github.com/kworr/smtp2tg
cd smtp2tg
cargo build --release

Configuration

Create smtp2tg.toml (see smtp2tg.toml.example for reference).
Get a Telegram Bot Token from @BotFather.
Get your chat ID (use @getidsbot or debug mode in Telegram client).

Example configuration

api_key = "123456789ABCdefGHIjklMNOpq"
api_gateway = "https://api.telegram.org"
listen_on = "127.0.0.1:1025"
unknown = "relay"
fields = ["date", "from", "subject"]
domains = ["example.com", "localhost"]

default = 0

[recipients]
"admin@example.com" = 12345678
"alerts@example.com" = -10012345678

To catch bounces (so they wouldn't stuck in upper mail server) make sure sender envelope address is real as required by mail library (actually not sure whether this applies to mailin). For example Postfix has to be tweaked like this:

$config_directory/main.cf: smtp_generic_maps = hash:$config_directory/generic

$config_directory/generic: "" postmaster@example.com <> postmaster@example.com

Actually not sure which one works...

Usage

Run

./smtp2tg -c /path/to/smtp2tg.toml

CLI arguments

Argument	Description	Example
`-h`, `--help`	Show help	`smtp2tg --help`
`-c`, `--config`	Path to config file	`smtp2tg -c config.toml`

Security

Important

Recommended usage: Run on 127.0.0.1 (localhost) only.
If exposing to a network:
- Restrict port access via firewall.
- Use TLS (e.g., via stunnel or nginx).
- Implement authentication (this software does not provide it).

Config file permissions

Set file permissions to 0600 (owner read/write only):

chmod 600 smtp2tg.toml

How it works

A client (e.g., Postfix) sends an email to listen_on (e.g., 127.0.0.1:1025).
smtp2tg parses the email and converts it to a Telegram message.
The message is sent to the specified chat (or default if address is unknown).

Example: Email → Telegram

Incoming email: ``` From: user@example.com To: admin@example.com Subject: Test

Hello, world! ```

Telegram message:

<blockquote expandable>
<u><i>Subject:</i></u> <code>Test</code>
<u><i>From:</i></u> <code>user@example.com</code>
<u><i>Date:</i></u> <code>Mon, 01 Jan 2024 12:00:00 +0000</code>
</blockquote>
<pre>Hello, world!</pre>