SPF, DKIM & DMARC: Definition & How They Secure Email Against Sender Fraud?

In this era of sophisticated modern cyberattacks, how can you be sure that the email in your inbox is really from your bank? Can the link within it really be trusted?

Avoiding this uncertainty is exactly what sender fraud protection through the implementation of SPF, DKIM, and DMARC is designed to do. This article will explain how the SPF, DKIM, and DMARC email authentication protocols help combat sender forgeries and will explore how to secure the inbox against fraudulent emails that may result in attacks on your organization leading to data theft, fraudulent wire transfers, significant, costly downtime and serious damage to your reputation.

Email Spoofing: A Favorite Technique among Cyber Criminals

Email Spoofing - a form of email fraud in which a malicious actor sends an email with a fraudulent “From” address - is a tactic frequently used in phishing attacks and other malicious email scams. In a spoofing attack, the sender forges an email header so that the client software displays the fraudulent sender address, which most users take at face value. By masquerading as an individual or organization that the recipient knows and trusts, attackers are more likely to successfully trick users into disclosing sensitive information, as recipients are more likely to click on a malicious URL, share credentials, install malware or wire corporate funds when it appears as if an email is from a known and trusted sender. Having an effective strategy in place to protect against email spoofing is critical, as spoofing is used in the majority of modern phishing scams, which account for over 90% of all cyberattacks.

What Are SPF, DKIM and DMARC and How Do These Protocols Protect Against Sender Fraud?

SPF, DKIM and DMARC are three protocols - or standards put in place for systems or devices to better communicate - used to verify sender identity and confirm the legitimacy of email communications. Let’s examine the purpose for each of these protocols and the mechanisms it employs to combat spoofing and sender fraud.

SPF Email Security

SPF (Sender Policy Framework) is an open standard that enables service providers to identify the source of each email message sent through their network. Email spoofing, or forging the sender's identity in an email message, can be used as part of a phishing scheme or as part of a spam campaign. SPF increases the likelihood that good messages will be delivered and spam blocked by providing Sender Policy Framework (SPF) information needed to allow mail servers to check the identity of senders who use your domain name.

DKIM Email Security

DKIM (DomainKeys Identified Mail) is a record that authenticates your organization’s domain name identity associated with an incoming email message, allowing the receiving mail server to verify that the message wasn’t altered in transit. DKIM uses public and private key pairs associated with your domain name to verify its identity on the Internet. This ensures that your outgoing SMTP servers have the right private key and prefix, enabling them to match a public DNS record that allows the receiving mail server to verify this information.

DKIM enables providers and recipients to associate a single domain or multiple domains with each signed message, and build a log of “trusted” and “untrusted” emails associated with given domains, IP addresses and From: identities. This provides them with the option of only allowing mail from “trusted” senders to be delivered.

DMARC Email Security

DMARC helps senders and recipients work together to create more secure email communications. The sender specifies the policy of their domain, and recipients will only accept mail from senders whose policies match their own. DMARC helps maintain the "domain reputation", which can be used by providers and recipients to determine whether an email received from a sender actually came from that sender and not a spoofed address.

DMARC helps you avoid phishing attacks by telling your email system which messages should be rejected, quarantined, or accepted. If the message fails DMARC evaluation, the receiver follows the instructions and lets you know if it was a false positive.

Limitations of SPF, DKIM and DMARC

While the SPF, DKIM, and DMARC protocols are instrumental in protecting against attacks that leverage sender fraud, they are not a “silver bullet” in the realm of email security. The three protocols work best when used together, but even then have potential deficiencies that must be considered prior to implementation. For instance, SPF records apply to Return-Path domains which are hidden in the header of an email, not the "From" address that an email client displays to the user. Thus, users generally pay attention to the “From” address, not the Return-Path domains. It also relies on the receiving domain actually checking the SPF record to ensure the email was sent from an authorized host. While SPF alone won't provide sufficient protection against sender forgeries, it’s an additional layer of protection that, combined with DKIM and DMARC, can improve delivery rates and prevent abuse.

DKIM tests use the domain name specified in an email's 'DKIM Signature' field, which is hidden from readers, and not the visible 'From' address. This allows threat actors to use a fake domain in the visible 'From' address while using their own hidden, DKIM address to sign the message.

In order to be truly effective in combating spoofing and sender fraud, these protocols should be implemented as part of a multi-layered email security solution managed by an expert provider who understands how to implement them to their fullest as part of a defense-in-depth approach to protecting sensitive information and preventing email fraud.

Keep Learning About Preventing Sender Fraud

Having an effective email security strategy in place that implements SPF, DKIM and DMARC is critical in setting up key standards and barriers for online communications, preventing sender fraud and spoofing - techniques used in the majority of modern cyberattacks. It is crucial to keep in mind that fortifying business email against today’s sophisticated attacks requires a defense-in-depth approach to security, and email authentication protocols should be implemented as part of a comprehensive strategy towards protecting business email, preferably managed by a reputable email security provider.

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