Basic usage

To derive your own SMTP-Server service with DATA processing simply do:

# Server class
class MySmtpd < MidiSmtpServer::Smtpd

  # get each message after DATA <message> .
  def on_message_data_event(ctx)
    # Output for debug
    logger.debug("[#{ctx[:envelope][:from]}] for recipient(s): [#{ctx[:envelope][:to]}]...")

    # Just decode message once to make sure, that this message ist readable
    mail = Mail.read_from_string(ctx[:message][:data])

    # handle incoming mail, just show the message subject
    logger.debug(mail.subject)
  end

end

Operation purposes

As already introduced, there is an endless field of application for SMTP services. Create your own SMTP Server as a mail gateway to clean up routed emails from spam and virus content or process incoming mails by your proper functions. Create your forwarding service to put messages into a service like Slack, Trello, Redmine, Twitter, Facebook, Instagram and others.

This source code shows the example to receive messages via SMTP and store them to RabbitMQ (Message-Queue-Server) for subsequent processings etc.:

  # get each message after DATA <message> .
  def on_message_data_event(ctx)
    # Just decode message once to make sure, that this message ist readable
    mail = Mail.read_from_string(ctx[:message])

    # Publish to rabbit
    @bunny_exchange.publish(mail.to_s, :headers => { 'x-smtp' => mail.header.to_s }, :routing_key => "to_queue")
  end

Working examples

This is a fully functional starter for a SMTP-Server service with DATA processing:

# frozen_string_literal: true

require 'midi-smtp-server'

# Server class
class MySmtpd < MidiSmtpServer::Smtpd

  # get each message after DATA <message> .
  def on_message_data_event(ctx)
    # Output for debug
    logger.debug("mail received at: [#{ctx[:server][:local_ip]}:#{ctx[:server][:local_port]}] from: [#{ctx[:envelope][:from]}] for recipient(s): [#{ctx[:envelope][:to]}]...")

    # handle incoming mail, just show the message source
    logger.debug(ctx[:message][:data])
  end

end

# Create a new server instance for listening at localhost interfaces 127.0.0.1:2525
# and accepting a maximum of 4 simultaneous connections per default
server = MySmtpd.new

# save flag for Ctrl-C pressed
flag_status_ctrl_c_pressed = false

# try to gracefully shutdown on Ctrl-C
trap('INT') do
  # print an empty line right after ^C
  puts
  # notify flag about Ctrl-C was pressed
  flag_status_ctrl_c_pressed = true
  # signal exit to app
  exit 0
end

# Output for debug
server.logger.info("Starting MySmtpd [#{MidiSmtpServer::VERSION::STRING}|#{MidiSmtpServer::VERSION::DATE}] (Basic usage) ...")

# setup exit code
at_exit do
  # check to shutdown connection
  if server
    # Output for debug
    server.logger.info('Ctrl-C interrupted, exit now...') if flag_status_ctrl_c_pressed
    # info about shutdown
    server.logger.info('Shutdown MySmtpd...')
    # stop all threads and connections gracefully
    server.stop
  end
  # Output for debug
  server.logger.info('MySmtpd down!')
end

# Start the server
server.start

# Run on server forever
server.join