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SPF, DKIM, DMARC: The 3 Pillars of Email Authentication

Email authentication is built on SPF, DKIM, & DMARC. These technical, essential terms will help you master email authentication and maintain brand reputation.


Effective February 2024, Google and Yahoo will have new requirements for bulk email senders on their platforms, one of which revolves around email authentication. This post walks you through what email authentication is and why it’s important.

As an email sender, you’ve always been told that it’s important to follow email best practices in order to get the best results from your email program. One of these best practices is to ensure that you’re properly authenticating your email messages. But the three pillars of email authentication, or SPF, DKIM, and DMARC, can be hard to understand (especially when there are already so many email acronyms!). Let’s look into these components of email authentication and why they’re so important.

Authentication is defined as “the process or action of proving or showing something to be true, genuine, or valid.” When we speak about email authentication, we’re talking about SPF, DKIM, and DMARC. These tools provide proof that an email message is genuine and that it’s coming from who it claims to be from.

So why does email authentication matter? Well, with the flood of spam and phishing messages floating around the email world, it becomes that much more important that your messages are properly provisioned and authenticated. Email authentication acts as your digital ID card and helps Mailbox Providers (MBPs) and spam filtering systems recognize your legitimate email.

The two primary authentication protocols that help validate that an email message comes from who it claims to come from are SPF and DKIM. Layered on top of SPF and DKIM is DMARC. DMARC uses SPF and DKIM and provides a set of instructions to receiving email servers with what to do if they receive unauthenticated mail.

Google and Yahoo’s new sender requirements say that all senders must use SPF and DKIM authentication. Bulk senders (sending more than 5,000 emails a day are also required to have a DMARC record setup on their FROM address domain.

Now that you have an overview of these three valuable email authentication tools, let’s dive into how each component works.

What Is Sender Policy Framework (SPF)?

Sender Policy Framework (SPF) is an authentication protocol that lists IP addresses in a DNS TXT record that are authorized to send email on behalf of domains.

A typical SPF record looks like this:

“v=spf1 ip4: ip4: -all”

When you send an email message, the receiving system will check to see if there is an SPF record published.

  • If there is a valid SPF record AND your sending IP is on the list, you PASS.
  • If the IP is NOT on the list, you FAIL the SPF check and could either be rejected or placed in the spam folder.

Unfortunately, SPF authentication has some limitations in terms of validating the message source. SPF also breaks when a message is forwarded and does not protect brands against bad actors who can spoof the display name or Friendly-From address. These limitations are some of the reasons why DKIM was created.

What is Domainkeys Identified Mail (DKIM)?

Think of domainkeys identified mail (DKIM) as an ID or passport that can verify who you are. When you are sent from your email server, the server attaches DKIM so the receiving server can verify you.

Technically speaking, DKIM authentication provides a method for validating a domain’s identity that is associated with a message through cryptographic authentication

It does this by using an encrypted key pair (one public in DNS and one private) to add a digital signature to every email message.

Receiving email servers use this DKIM signature to both validate the authenticity of the sender and to identify if the message was changed or altered during transit. DKIM-signed messages provide Mailbox Providers (MBPs) with trust that the message is authentic and is not being spoofed.

MBPs’ internal filtering algorithms use SPF and DKIM along with other factors to determine if an email should be placed in the inbox, spam folder, or be rejected. However, both SPF and DKIM don’t allow domain owners to instruct MBPs how to treat a message if the authentication checks can’t be validated.

To help tell MBPs know what to do if DKIM and/or SPF fail, senders can implement DMARC. DMARC leverages both SPF and DKIM and provides instructions from the domain owner about what to do with unauthenticated email.

What is Domain-based Message Authentication, Reporting & Conformance (DMARC)?

Our third authentication component, Domain-based Message Authentication, Reporting & Conformance (DMARC), is an email authentication, policy, and reporting protocol. It helps domains address domain spoofing and phishing attacks by preventing unauthorized use of the domain in the Friendly-From address of email messages. DMARC allows the domain owner to specify how unauthenticated messages should be treated by MBPs. This is accomplished by what is known as a “policy” that is set in the DMARC DNS record. The policy can be set to one of three options: NONE, QUARANTINE, and REJECT.

  • Policy = (p=none): no action and message delivered as normal
  • Policy = (p=quarantine): places the message to spam/junk/quarantine folder
  • Policy = (p=reject): the message rejected/bounced

The R in DMARC is for the Reporting component of the protocol. These reports allow the domain owner to see where all email using their domain in the FROM address is being sent from.

How Do You Get Started With SPF, DKIM, and DMARC?

The first step to configuring SPF, DKIM, and DMARC is to reach out to your support team and check to see if you are already using email authentication. If you aren’t, they will have the necessary documentation to help you set up the correct authentication for their platform. If you are, you can check that task off your list!

Enabling email authentication isn’t only an email best practice to help get your email delivered, but they are critical tools in helping to protect your brand’s reputation by limiting the chances that an unauthorized sender can successfully use your domain without your consent or knowledge.

This post was originally published September 23, 2021 but has been reviewed and updated for accuracy as of January 2024.

Dean Canellos

Dean Canellos is the Manager of the Deliverability Operations team at Higher Logic. He has been with Higher Logic for 15 years working on all aspects of email deliverability. His team is involved in presales vetting, onboarding, provisioning, and ongoing support of deliverability issues. His team provides Higher Logic customers with email best practices to help them achieve their email program goals. They also monitor the Higher Logic IP space against blocklists, manage the Higher Logic email sending servers, IPs, and provide DNS management.