Email authentication

Email authentication acts as a digital ID card for your domain. When you send an email, receiving servers check these protocols to confirm you are the authorized sender. If the checks pass, the email is more likely to reach the inbox.

The process relies on the Domain Name System (DNS). By publishing specific records on your domain, you publicly declare which servers are allowed to send emails on your behalf and how receiving servers should handle messages that fail these checks.

For newsletter creators, proper authentication is non-negotiable. Major inbox providers require strict authentication to protect their users from spam and phishing attacks.

Failing to authenticate a custom sending domain usually results in emails being routed to the spam folder or rejected entirely. It is the foundational step in building a positive sender reputation and ensuring subscribers actually receive your content.

In the early days of email, the Simple Mail Transfer Protocol (SMTP) lacked built-in mechanisms to verify sender identity. This flaw allowed spammers to easily forge the sender address, leading to widespread phishing and spam.

To combat this, the industry developed a series of protocols over the years. SPF and DKIM emerged first to address authorization and message integrity. Later, DMARC was introduced to provide a unified policy framework, giving domain owners control over how unauthenticated mail is handled.