Email authentication: Why it matters and how SPF, DKIM, and DMARC ensure security
The emails you send out to your clients are not just about informing them about your business but creating a relationship with them. Imagine what would happen if the emails that go from your end rarely reach them? Or even worse, what if a hacker dupes your customers by sending them emails on your behalf? That would ruin all the trust you’ve built so far. Not to mention, much more severe effects, such as data breaches, losses in finance, and loss of reputation, would follow.
When the stakes are so high, one thing’s certain: you should not and cannot be complacent about email security. But, we also understand that email security is a complex endeavor and requires a strategic approach.
Unless you know the technicalities of the email infrastructure, you may think your emails are inherently secure. However, the fact remains that emails are quite vulnerable to various kinds of attacks, and the basic protection that mail servers offer becomes ineffective in this regard. And this brings us to email authentication.
In this article, we’ll talk about why you and your organization should take email authentication seriously and how SPF, DKIM, and DMARC come together to protect your emails.
Is email authentication even necessary?
Now that you know emails aren’t inherently secure, the answer is obvious. But let us dig deeper and understand why an extra layer of security is essential in email communication.
The problem is that email was never designed to be what it is today. In fact, the Simple Mail Transfer Protocol, which is the foundation of email communication, makes no effort to verify whether the sender of a message is who they claim to be. This loophole opened doors for malicious attacks like spoofing, phishing, and malware injections.
Every SMTP email message has two fundamental parts: the message envelope and the message content. Although the former is defined as the source of information used in sending and receiving messages by the email server, the recipients never get to see this envelope since it is generated during the time of transmission. Instead, they only see the content of the message, such as the message header and the body. This design creates multiple sender values for the message and makes it easier for a cyber attacker to manipulate one sender value.
The other part of the email message is the FROM address, commonly referred to as the envelope sender or Return Path. This part is used to transmit messages between SMTP servers. It records the address in case the delivery fails and a bounce message has to be generated.
It is important to note that this is not the address recipients often see in their inboxes. What the recipients see in the message header is actually the From address (RFC 5322), which they tend to trust as the actual sender’s address.
It is here that authentication protocols like SPF, DKIM, and DMARC come in, as they fill the gaps left by SMTP. They offer scope for email providers and recipients to authenticate mail sources and defend against spoofing and phishing attacks.
How do SPF, DKIM, and DMARC work together to secure emails?
You already know that email authentication is no longer a ‘good-to-have’ feature in your cybersecurity strategy; it’s an absolute must. Speaking of email authentication, the three most trusted protocols used by security teams worldwide are— SPF, DKIM, and DMARC. Each one serves a distinct role in verifying the sender’s authenticity and securing your email communications. When deployed together, they create a more layered and comprehensive defense against email-based attacks, making it harder for attackers to impersonate your domain or compromise your communications. Let’s take a look at them and how they work together.
SPF (Sender Policy Framework)
This protocol allows domain owners to specify all the servers authorized to send emails on behalf of their brand. So, when the receiving server receives an email, it checks for the sender’s SPF record to verify whether the server from which the email came is listed in it. This prevents other servers from forging an email and sending it under your domain name.
DKIM (DomainKeys Identified Mail)
DKIM attaches a unique digital signature to your message, which the recipient’s mail server verifies using a public key published in your domain’s DNS records. This verifies that the email wasn’t tampered with in transit, so you’re assured of the origin and integrity of the message.
How DKIM supports SPF
In case an email fails SPF authentication, DKIM steps in to verify its authenticity. This usually happens when you rely on an email hosting service sending emails from different domains, but the ‘MAIL FROM’ is the same. It also occurs when a server forwards a message. In this case, the DKIM signature of the message remains unchanged, so even if SPF does not verify the sender, DKIM does so.
DMARC (Domain-based Message Authentication, Reporting, and Conformance)
DMARC is based on the verification results of SPF and DKIM. It lets you set policies for handling emails that fail authentication checks. With DMARC, you can tell receivers to quarantine or reject anything suspicious and receive reports in case unauthorized attempts to make use of your domain have succeeded.
How DMARC helps SPF and DKIM
The problem is that SPF does not check if the domain mentioned in the ‘MAIL FROM’ address used during email transmission actually matches the domain in the ‘From’ address that the receivers see. Similarly, DKIM also does not check whether the domain that signed the email matches the ‘From’ address domain. DMARC bridges this gap by ensuring that the domain in the ‘From’ address is consistent with the domains validated by SPF and DKIM. It ensures that an email not only passes SPF and DKIM checks but also verifies if it is coming from the domain it claims to be coming from, thus providing an added layer of security against spoofing and phishing.
