Deliverability is a moving target, so you can’t really rely on your delivery metrics from last week. Why? The SPAM Scoring Industry is a kind of monoculture th

Deliverability is a moving target, so you can’t really rely on your delivery metrics from last week. Why? The SPAM Scoring Industry is a kind of monoculture that will impede or cancel delivery of messages. Most big email providers outsource SPAM scoring to a third party like Symantec or Brightworks. And when your email is found offensive by Brightworks with one of their clients, you’re banned on all of their clients. Part of how SPAM scorers gather intel us by hooking into the CFL system so they get a notification when a user hits the junk button to delete an email. Another way is by checking for mass duplication in your emails. Another way is tracking open rates via the email provider’s UI sending metrics to the scorer’s APIs. And then there’s the CIDR block lists they coordinate and distribute as a courtesy for their customers. So you might be able to deliver to @gmail.com and then @yahoo.com won’t even take a connection from your server’s IP. Why does all this happen? According to my friend who works for a midrange ISP on their email service, they have about 120PB to store real email. And the amount of SPAM they reject outright (never reaches any box, not even the junk box) is 93% of all their email traffic. They simply can’t afford to store all the SPAM.