issue.rb

  # Returns the mail adresses of users that should be notified
  def recipients
    notified = project.notified_users
    # Author and assignee are always notified unless they have been locked
    notified << author if author && author.active? && author.notify_about?(self)
    notified << entered_by if entered_by && entered_by.active? && entered_by.notify_about?(self)
    notified << assigned_to if assigned_to && assigned_to.active? && assigned_to.notify_about?(self)
    notified.uniq!
    # Remove users that can not view the issue
    notified.reject! {|user| !visible?(user)}
    notified.collect(&:mail)
  end

user.rb

  # Utility method to help check if a user should be notified about an
  # event.
  #
  # TODO: only supports Issue events currently
  def notify_about?(object)
    case mail_notification.to_sym
    when :all
      true
    when :selected
      # Handled by the Project
    when :none
      false
    when :only_my_events
      if object.is_a?(Issue)&& (object.author == self || object.entered_by ==self || object.assigned_to == self)
        true
      else
        false
      end
    when :only_assigned
      if object.is_a?(Issue) && object.assigned_to == self
        true
      else
        false
        end
    when :only_owner
      if object.is_a?(Issue) && object.author == self
        true
      else
        false
      end
    when :only_owner_or_creator
      if object.is_a?(Issue) && (object.author == self || object.entered_by == self)
        true
      else
        false
      end
    else
      false
    end
  end