Mailchimp currently sends about 600 million emails every day, and all of those users expect their campaigns to be delivered immediately. Conveniently, that’s exactly what we want, too. So how do we make it happen? We approach sending those 600 million emails like this golden retriever approaches a big plate of spaghetti: with no fear, just wolfing it all down super fast in big chunks.
Our sending infrastructure is designed to turn large campaigns into smaller “payloads” to get them out the door much faster. When you click Send in the Campaign Builder, you’re actually telling Mailchimp to start biting off parts of your campaign. As each payload is created, it’s immediately routed to our Mail Transfer Agents (MTAs) and queued for delivery. We organize this based on contact ratings, so the most engaged subscribers in your campaign are first in line.
For larger campaigns, like the one in the following graph, payloads usually only include about 10,000 recipients each. Here, since the MTA isn’t waiting around for one giant payload of 470,000 to be built and queued at once, deliveries can start immediately.