MailBuilder

MailBuilder is a library for building RFC compliant MIME messages, with support for text and HTML emails, as well as attachments.

require 'rubygems'
require 'mail_builder'

mail = MailBuilder.new
mail.to = "joe@example.com"
mail.text = "Body"

sendmail = IO.popen("#{`which sendmail`.chomp} -i -t", "w+")
sendmail.puts mail
sendmail.close

require 'net/smtp'

Net::SMTP.start("smtp.address.com", 25) do |smtp|
  smtp.send_message(mail.to_s, mail.from, mail.to)
end

One of the key advantages to using MailBuilder over other libraries (such as MailFactory) is that costly operations - generating boundaries, reading attached files, etc. - are delayed until the physical message is built (by calling build or to_s).

This gives you the freedom to generate many thousands of emails with almost no time-cost. The emails could then be passed to some external system - DRb, database - for final delivery.

10_000.times do
  mail = MailBuilder.new('to' => 'joe@example.com')
  mail.html = View.new("mailers/large_mailer")
  mail.attach("large_file.pdf")

  ExternalMailServer.send!(mail)
end

The external process would then build the email, at which point the view would be rendered and attachments read, while the local process would complete in very little (on my machine, sub-second) time.