About

This projects provides a dockerized smtp server that forwards incoming mails as signal messages.

Quickstart

• Checkout this repository
• Create subdirectory data
• Start/Update services $ docker-compose up --build --force-recreate -d --remove-orphans
• Optionally: Setup signal-cli - register numbers, ...
• Get auto-created smtp credentials: $ cat ./data/smtp2signal/smtp2signal.token
• Done. The smtp server now listens at port 8025 (all interfaces). See Signal Message Routing for howto send messages.

Signal Message Routing

The smtp server evaluates the first mail recipient's address:

• The domain part (right side of @) must be valid but is ignored otherwise
• The local part (left side of @) is parsed as query string with the following exceptions:
  • + is treated literally and not replaced by space
  • -- maybe used to substitute = if not supported by mail client
• If an argument is expected only once, but given multiple times, the last argument value takes precedence. The following arguments are supported:
  • from: required once - sender account number; must be registered for use with signal-cli, otherwise sending the signal message will be refused
  • to: required at least once if not to_group is given - phone number(s)/account name(s) of recipient(s)
  • to_group: required once if to is not given - recipient group id in signal-cli format (as per signal-cli listGroups subcommand output; using url escaping where necessary, e.g. = escaped as %3D)
  • omit_subject: optional boolean - mail subject will not be forwarded if true, defaults to false
  • omit_body: optional boolean - mail body will not be forwarded if true, defaults to false
  • body_separator: optional string - characters to insert between subject line and body, defaults to \n\n
  • lines: optional set of single line numbers, ranges of line numbers (2-4 end inclusive), or the term all - for each argument, the referenced lines will be appended to the signal message, defaults to all

Examples:

• from--+49123456789&to--+49987654321&to--+49192837465@example.com - message forwarded to +49987654321 and +49192837465 using +49123456789 as sender
• from--+49123456789&to_group--+xh18rfD4ewA0AikA+Yi5tfrSaikS5fCfnTt5VEJAaQ%3D&--omit_body=true@example.com - message subject forwarded to given group using +49123456789 as sender

Setup signal-cli

Numbers need to be register with signal-cli. The easiest way to to this is interact with the command line signal-cli client. This is only possible if the smtp2signal gateway is not running (more specifically the rest api container).

• Stop smtp2signal: $ docker-compose stop
• Run signal-cli container: $ docker-compose run -u signal-api -it --entrypoint bash signal-cli-rest-api
• Configure signal-cli: Register number, ...
• Restart smtp2signal $ docker-compose up -d

Note: Make sure the proper signal-cli data directory is bind-mounted for the signal-cli configuration data to be preserved.