sirrahd/smtp-to-line

Relays incoming email messages to LINE Messenger

SMTP to LINE

Relays incoming emails to LINE messenger. Inspired by SMTP to Telegram.

Use it as an SMTP server for webcams, selfhosted services, development environments, and as a smarthost to receive emails as LINE notifications.

Getting started

1. Set up your LINE developer account and channel: https://developers.line.biz/en/docs/messaging-api/getting-started/
2. Retrieve your user ID and channel access token from the channel in the LINE developers console (Basic Settings->Your user ID; Messaging API-> Channel access token)
3. Run smtp-to-line in a Docker container by cloning this repository and running this command:

docker run \
    --name smtp-to-line \
    -e SL_LINE_CHANNEL_ACCESS_TOKEN=<TOKEN> \
    -e SL_LINE_USER_ID=<ID> \
    $(docker build -q .)

4. smtp-to-line listens for incoming SMTP traffic on port 8025

Note: LINE has a 500 per month limit on free messages sent via its API (see Messaging API overview).

Additional features

Customized message template

Define a custom message template for LINE notifications with the environment variable SL_MESSAGE_TEMPLATE. Available variables:

• {sender}
• {recipient}
• {subject}
• {text}

Default: SL_MESSAGE_TEMPLATE="{subject}\nFrom: {sender}\n\n{text}"

Hosting file attachments

smtp-to-line can extract images, attachments, and html messages from emails to the folder /smtp-to-line/data, which can then be hosted with a web server. Define an SL_WEB_ROOT to define a root URL where these files are hosted.

Example: SL_WEB_ROOT="https://example.com/smtp-to-line/"

STARTTLS encryption

Specify the path to a SL_SSL_CERT_FILE and SL_SSL_KEY_FILE in PEM format to enable STARTTLS encryption.

Alternatively, smtp-to-line can use the first certificate in a Traefik resolvers file with the SL_TRAEFIK_CERT_PATH environment variable.

Authentication

By default smtp-to-line will accept any SMTP request and fake successful authentication if credentials are provided. To require real authentication for all requests, provide space-separated uesrnames and passwords in the SL_AUTH environment variable.

Example: SL_AUTH="user1 password1 user2 password2"

Docker Compose example

These example docker-compose services enable all features and provide an nginx web server for hosting attachments.

  smtp-to-line:
    build: https://github.com/sirrahd/smtp-to-line.git
    ports:
      - "587:8025"
    environment:
      SL_LINE_CHANNEL_ACCESS_TOKEN: "TOKEN"
      SL_LINE_USER_ID: "USERID"
      SL_WEB_ROOT: "http://example.com/"
      SL_SSL_CERT_FILE: "/certificates/cert.pem"
      SL_SSL_KEY_FILE: "/certificates/key.pem"
      SL_AUTH: "user1 password1 user2 password2"
    volumes:
      - "./certificates:/certificates:ro"
      - "./web:/smtp-to-line/data"
  nginx:
    image: docker.io/library/nginx
    ports: "80:80"
    volumes:
      - "./web:/usr/share/nginx/html"