How DMARC WORKS

DMARC (Domain-based Message Authentication, Reporting, and Conformance) works by verifying if an email’s SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) align with the domain it claims to be from. Here’s how it operates:

1. Alignment Check: DMARC ensures that SPF and/or DKIM align with the “From” domain, confirming the email’s authenticity.
2. Policy Enforcement: Based on the result, DMARC applies a policy specified by the domain owner: none (monitor only), quarantine (mark as spam), or reject (block email).
3. Reporting: DMARC generates reports on email authentication results, which are sent back to the domain owner for review.

This process improves email security by reducing spoofing and phishing attacks while giving domain owners visibility into potentially fraudulent emails.

DMARC relies on two main email authentication protocols:

1. SPF (Sender Policy Framework): SPF checks if the IP address sending the email is authorized by the domain’s DNS records to send emails on its behalf.
2. DKIM (DomainKeys Identified Mail): DKIM adds a digital signature to emails, verifying that the message content has not been tampered with and confirming the sender’s identity.

DMARC combines these two protocols by aligning their results with the “From” address in an email and defining actions if they fail, such as rejecting or quarantining the message.

Here’s how SPF and DKIM work in email authentication:

SPF (Sender Policy Framework)

• Purpose: SPF verifies the sending server’s IP address against authorized IPs listed in the sender domain’s DNS.
• Process: When an email is received, the recipient’s server checks the SPF record to ensure the IP is allowed to send emails for that domain.
• Result: If the IP isn’t listed, the email may be flagged as suspicious or rejected.

DKIM (DomainKeys Identified Mail)

• Purpose: DKIM confirms that the email content hasn’t been altered and that it’s truly from the claimed sender.
• Process: The sender’s server adds a DKIM signature (an encrypted hash of the email) in the email header. The recipient’s server retrieves the DKIM public key from DNS to verify the signature.
• Result: If the signature matches, the email is verified; if not, it’s likely spoofed or altered.

Together, SPF and DKIM provide layers of email authentication, with DMARC aligning these checks to enforce policies like blocking unauthenticated emails.

Yes, SPF and DKIM keys are visible in DNS records if you have access to a domain’s DNS settings. Here’s how to view and understand them:

SPF Record

SPF records are stored as DNS TXT records. To view them:

• Use DNS lookup tools (like nslookup or dig) to query the SPF TXT record for a domain, e.g., v=spf1 include:_spf.example.com -all.

DKIM Public Key

DKIM keys are also published in DNS as TXT records.

• Each DKIM key has a unique selector (e.g., selector._domainkey.example.com), which is used to retrieve the public key associated with that selector.

Both of these records can be viewed using online DNS lookup tools if you know the domain and selector (for DKIM).

In the backend, SPF and DKIM use DNS to authenticate emails:

SPF

1. Email Sent: When an email is sent, the recipient’s server checks the sending domain’s DNS for an SPF TXT record.
2. IP Match: It verifies if the sending server’s IP matches the authorized IPs listed in the SPF record.
3. Action: If the IP matches, the email is authenticated; otherwise, it may be flagged or rejected.

DKIM

1. Email Signature: The sender’s server generates a DKIM signature using a private key and adds it to the email header.
2. Verification: The recipient’s server retrieves the public key from the sender’s DNS using the selector provided in the header.
3. Match Check: If the decrypted signature matches, the email is verified; if not, it might be altered or spoofed.

These processes ensure email authenticity by aligning records stored in DNS with the sender’s identity.

 

Attackers exploit SPF, DKIM, and DMARC through several methods:

1. Domain Spoofing: Attackers may use domains similar to trusted ones (e.g., replacing letters) to bypass SPF/DMARC.
2. Key Mismanagement in DKIM: Using weak or outdated keys, or failing to rotate them, allows attackers to exploit DKIM, potentially forging valid-looking signatures.
3. Insufficient Policy in DMARC: Weak DMARC policies (like “none”) allow malicious emails to pass through, as they don’t enforce quarantine or rejection.
4. DNS Exploits: Attackers can potentially hijack or spoof DNS records, redirecting SPF or DKIM checks to unauthorized IPs.

Preventing these attacks requires robust security practices, monitoring, and regular DNS and key management.

Attackers can gain access to SPF, DKIM, or DMARC systems mainly through these methods:

1. Phishing and Social Engineering: They can trick administrators into revealing login credentials, allowing access to DNS settings to alter SPF or DKIM records.
2. DNS Hijacking: If attackers exploit vulnerabilities in DNS providers or intercept DNS queries, they can redirect records, leading to unauthorized servers.
3. Insecure Key Management: Weak or poorly secured DKIM keys can be cracked or stolen, allowing attackers to forge email signatures.
4. Weak Passwords on Control Panels: If control panels managing DNS records aren’t secured with strong authentication, attackers can easily access and alter records.

Strengthening security controls, regular monitoring, and using multi-factor authentication on DNS and email systems can mitigate these risks.