In the universe of message queues, an email-per-sale queue is not going to be your problem. Think of the queue-as-message-bus pattern -- very common. You don't

In the universe of message queues, an email-per-sale queue is not going to be your problem. Think of the queue-as-message-bus pattern -- very common. You don't want to have a service with millions of pending messages to process, it forces you into painful, slow recovery, or making the tough choice of dropping everything. Anyway, great write up, and happy new year!