Transactional Email “Send Once” with Delivered Marker

                  class Emails::SendOnce
  def call(key:, &block)
    DeliveredEmail.create!(key: key)
    yield
  rescue ActiveRecord::RecordNotUnique
    false
  end
end

                

                  Emails::SendOnce.new.call(key: "receipt:order:#{order.id}") do
  ReceiptMailer.order(order.id).deliver_now
end