gistfile1.rb

# config/initializers/email_logger.rb
class EmailLogger
  def self.delivered_email(email)
    EmailLog.create!(
      :from => email.from,
      :to => email.to,
      :subject => email.subject,
      :body => email.body.inspect,
      :date => email.date
    )
end

Mail.register_observer(EmailLogger)


# app/models/email_log.rb
class EmailLog
  include Mongoid::Document
  field :from, :type => Array
  field :to, :type => Array
  field :subject
  field :body
  field :date, :type => DateTime
end

you are missing a closing end to the delivered_email method ;)