FastMailer

FastMailer is a collection of helpers that aims to help with sending email. Specifically, it allows for convenient configuration and better throughput when sending multiple mails using SMTP.

Configuration

The FastMailer senders are configured with a regular options hash, pretty much what you'd expect:

FastMailer::SMTP.new({
  :host => 'mail.authsmtp.com',
  :port => 2525,
  :authentication => :cram_md5,
  :domain => 'mydomain.com',
  :username => 'username',
  :password  => 'password'
})

Something I've found very convenient, however, is to let the gem read the default configuration from your home directory. For instance, let's assume we put:

{
  :host => 'mail.authsmtp.com',
  :port => 2525,
  :authentication => :cram_md5,
  :domain => 'mydomain.com',
  :username => 'username',
  :password  => 'password'
}

into ~/.config/smtp.rb, you could then achieve the same result by simply not providing any options at all. This makes it really easy to write small scripts that send email without having to worry about configuration.

Sending mail

When sending a lot of mail, every second counts - especially if you don't have your SMTP server close by. To reduce the time it takes to send a lot of email, we can send multiple emails using a single connection.

mail = build_mail_somehow # mail is a Mail instance (as from the mail gem)

FastMailer::SMTP.new.open do |smtp|
  smtp.deliver mail
  mail.to = 'another@recipient.com'
  smtp.deliver mail
end

Testing

To enable testing, first run

FastMailer.test_mode = true

This will cause FastMailer::SMTP to use FastMailer::MockSMTP rather than Net::SMTP. You can then find your sent emails in FastMailer::MockSMTP.deliveries.

Parallelisation

To send a large number of emails, you can use the FastMailer::Mailer class. Create it as an SMTP instance, but include an additional option :max_connections. When calling send_all with a mail iterator (any object yielding Mail instances on :next), :max_connections threads will be spawned, sending mail from the generator in parallel.

emails = [mail_1, mail_2, ..., mail_n]
mailer = FastMailer::Mailer.new
mailer.send_all emails.to_enum

Note that the generator must not return modified instances of the same object multiple times, since up to :max_connections mails will be processed at the same time.

The :send_all call will not return until all mails have been sent. At this point, all spawned threads will have stopped.

Coming features

• Logging: When sending large batches, sometimes things go wrong. If we keep track of which mails have been sent and which have failed, we reduce the risk of finding ourselves wondering which of our users have received the message and which we need to send to.