DMARC email authentication is an important element of phishing defenses, but what is DMARC email authentication, what does it do, and how does it protect against email impersonation attacks?

There is some confusion about what DMARC email authentication is and what it can do. In this post we explain in clear English what DMARC means and why it should be part of your anti-phishing defenses.

What is DMARC

DMARC is short for Domain-based Message Authentication, Reporting, and Conformance. Its purpose is to make it harder for threat actors to conduct phishing attacks that spoof brands and get those messages delivered to inboxes. DMARC is a critical component of email cybersecurity that reduces an attacker’s ability to get email threat to an end user’s inbox.

With DMARC, organizations can create a record of who is authorized to send emails from their domain. This helps to prevent misuse of a company brand in phishing campaigns.

If DMARC is implemented on email, a business can have all incoming emails checked against DMARC records and any email that fails the check can be subjected to certain actions.

The message can be delivered as normal with a warning and the email will be included in a report of emails that failed the check. The message could automatically be sent to quarantine for manual approval before delivery is made. Alternatively, the message could be rejected or subjected to a custom policy. An organization can select the best policy to adopt based on their level of risk tolerance.

DMARC will not stop all phishing emails from being delivered, but it is an important measure to implement to stop email spoofing and reduce the number of phishing emails that reach inboxes. DMARC is just one of several rules that are used to determine whether emails are genuine and should be delivered or if the messages have been sent from an unauthorized user.

Sender Policy Framework (SPF), DomainKeys Identified Mail (DKIM), and DNS records are also used to determine whether the email server being used is authorized to send emails for the organization. 

What is  Sender Policy Framework (SPF)

The Sender Policy Framework (SPF) is an email-authentication technique used to restrict who can send emails from your domain. It allows your mail server determine when a message comes from the domain that it uses. SPF has three major elements: a policy framework, an authentication method and specialized headers to convey the information.

An email message contains two sender addresses:

  1. The From:header, displaying the name and email address of the sender
  2. The Envelope From:or Return-Path email address.

Both types of sender addresses can be easily spoofed.

SPF uses a DNS record to verify the Envelope From: only. This means that if a spammer spoofs the Envelope From: address using a domain where SPF is enabled, the mail will be caught by the receiving server. If the spammer spoofs the From: header, SPF will not catch this. The SPF record indicates which email servers are authorized to send mail on behalf of a domain. This would be the organization itself and any third parties, such as marketing companies.  The SPF record is a DNS TXT record that includes IP addresses and hostnames that are allowed to send emails from a particular domain. The SPF record is the first thing checked by DMARC rules.

Together with the DMARC related information, this gives the receiver (or receiving systems) information on how trustworthy the origin of an email is. SPF is, just like DMARC, an email authentication technique that uses DNS (Domain Name Service). This gives you, as an email sender, the ability to specify which email servers are permitted to send email on behalf of your domain.

DKIM

DKIM is more advanced and uses a TXT record and asymmetric public-private key encryption. With DMARC enabled, the signature is encrypted with the public key and the key is published on DNS servers. The domain’s private key is then used at the recipient’s email server for verification.

If DKIM is enabled, the public key-encrypted signature is compared with the message that is decrypted using a newly generated key to confirm that the message has not been altered. DKIM also confirms that the sender is from the listed domain and that the sender has not been spoofed.

DMARC offers a much greater level of protection than SPF and is more dependable, so both should be implemented. Both SPF and DMARC are incorporated into SpamTitan to better protect users from email spoofing attacks. Enabling SPF, DKIM and DMARC will help greatly reduce the amount of spoof emails recieved, and that is only good.

To find out more about improving your email security defenses, contact the TitanHQ team today.