remailer

Client/Server Mail Networking Library for SMTP and IMAP

This is an EventMachine Connection implementation of a high-performance asynchronous SMTP client. Although EventMachine ships with a built-in SMTP client, that version is limited to sending a single email per client, and since establishing a client can be the majority of the time required to send email, this limits throughput considerably.

The Remailer system consists of the Remailer::Connection class which works within the EventMachine environment. To use it, create a client and then make one or more requests to send email messages.

EventMachine.run do
  # Establish a client to a particular SMTP server and send debugging
  # messages to STDERR.
  client = Remailer::SMTP::Client.open(
    'smtp.google.com',
    debug: STDERR
  )

  # Send a single email message through the client at the earliest
  # opportunity. Note that the client will need to be fully
  # established first and this may take upwards of ten seconds.
  client.send_email(
    'from@example.net',
    'to@example.com',
    email_content
  )

  # Send an additional message through the client. This will queue up
  # until the first has been transmitted.
  client.send_email(
    'from@example.net',
    'to@example.com',
    email_content
  )

  # Tells the client to close out when finished.
  client.close_when_complete!
end

A Proc can be supplied as the :debug option to Remailer::Connection.open and in this case it will be called with two parameters, type and message. An example is given here where the information is simply dumped on STDOUT:

client = Remailer::SMTP::Client.open(
  'smtp.google.com',
  debug: lambda { |type, message|
    puts "#{type}> #{message.inspect}"
  }
)

The types defined include:

• :send - Raw data sent by the client
• :reply - Raw replies from the server
• :options - The finalized options used to connect to the server

This callback procedure can be defined or replaced after the client is initialized:

client.debug do |type, message|
  STDERR.puts "%s> %s" % [ type, message.inspect ]
end

It's also possible to define a handler for when the message queue has been exhausted:

client.after_complete do
  STDERR.puts "Sending complete."
end

The call to send a message can also take a callback method which must receive one parameter that will be the numerical status code returned by the SMTP server. Success is defined as 250, errors vary:

client.send_email(
  'from@example.net',
  'to@example.com',
  email_content
) do |status_code|
  puts "Message finished with status #{status_code}"
end

A status code of nil is sent if the server timed out or the connection failed.

In order to run tests, copy test/config.example.yml to test/config.yml and adjust as required. For obvious reasons, passwords to SMTP test accounts are not included in the source code of this library. Any Gmail-type account should serve as a useful test target.

This software is currently experimental and is not recommended for production use. Many of the internals may change significantly before a proper beta release is made.

Copyright (c) 2010-2023 Scott Tadman, PostageApp Ltd.