Well, actually no. The vast majority of bulk email is done via 3rd party providers like constant contact or mail chimp because delivery is important. You can'

Well, actually no. The vast majority of bulk email is done via 3rd party providers like constant contact or mail chimp because delivery is important. You can't just check an address--you have to check against the particular mailing list, email address and account which means you'd have to basically have to have the database. Otherwise, if I unsubscribe from "Megous Monthly Mailer" I'll stop getting the announcements from my kid's school with useful info like what the first day of school for my kid is. So you need to know the account, the mailing list that was unsubscribed, the email address. Of course, the system is architected for high-volume, and scheduled email. Delivery volumes can be in the billions per minute. Anything too crazy and your service level is destroyed. Queues are designed for high-volume queuing, not search, or retrieval. There's no "query API" for rabbitMQ, for example. All of this is easy if we hand-wave away the requirements for high volume email delivery.