Authentication is a high-tech way of signing your emails to show it’s not a forgery. It’s basically a string of code you have to add to your email (it’s built-in to MailChimp, and it’s free for all customers). The idea behind authentication has always been that eventually, ISPs may start blocking emails that are not authenticated (or at least slow those emails down). This might eventually stop all the stupid phishing scams you get in your inbox from people pretending to be eBay, or PayPal, or your local bank.

But most ISPs have not gone so far as to block non-authenticated emails…

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