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Understanding SPF and DKIM Alignment in DMARC Monitoring

What is SPF and DKIM Alignment in DMARC Monitoring?

In email security, DMARC plays a key role by using two existing authentication methods: SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail). To understand how DMARC enhances email security, it’s important to grasp what SPF and DKIM alignment mean.

What does SPF mean?

SPF is an email authentication method designed to detect and block email spoofing. It works by allowing domain owners to specify which mail servers are permitted to send email on behalf of their domain. When an email is received, the recipient's mail server checks the SPF record to verify if the sending server is authorized.

Example: If the domain example.com has an SPF record that states only mail.example.com is allowed to send emails, any email claiming to be from example.com but sent from a different server would fail the SPF check.

What is DKIM?

DKIM is another email authentication method that enables the receiver to verify that an email was actually sent and authorized by the owner of that domain. It works by attaching a digital signature, linked to a domain name, to each outgoing email message. This signature can be verified by the recipient to confirm the email has not been altered during transit and is from a legitimate source.

Example: When example.com sends an email, a DKIM signature is added to the email header. The recipient’s server uses the public key published in the DNS records of example.com to verify the signature.

What is Alignment?

For DMARC to recognize an email as authenticated, the email must pass either the SPF or DKIM check, and the domains in these checks must align with the domain in the "From" address. Alignment ensures that the domains match or are a subdomain, adding an extra layer of security.

There are two kinds of alignment: strict and relaxed.

1. Strict Alignment:

  • SPF Strict Alignment: The domain in the "From" address must exactly match the domain in the SPF check.
  • DKIM Strict Alignment: The domain in the "From" address must exactly match the domain in the DKIM signature.

2. Relaxed Alignment:

  • SPF Relaxed Alignment: The domain in the "From" address must be a subdomain of the domain in the SPF check.
  • DKIM Relaxed Alignment: The domain in the "From" address must be a subdomain of the domain in the DKIM signature.

Why is Alignment Important?

Alignment is important because it stops attackers from spoofing your email addresses. Without alignment, an attacker could pass SPF or DKIM checks using their own domain, making the email seem genuine. By enforcing alignment, DMARC makes sure only authorized servers can send emails on your domain's behalf.

Implementing SPF and DKIM Alignment

1. Configure SPF Records:

  • Publish an SPF record in your DNS settings that specifies which mail servers are authorized to send emails on your behalf.
  • Make sure the domains in the SPF record match the domain in the "From" address.

2. Set Up DKIM:

  • Generate a pair of cryptographic keys (private and public).
  • Publish the public key in your DNS settings as a TXT record.
  • Configure your mail server to sign outgoing emails with the private key.
  • Ensure that the domain in the DKIM signature aligns with the domain in the "From" address.

3. Enable DMARC:

  • Publish a DMARC record in your DNS settings.
  • Specify the alignment mode (strict or relaxed) for SPF and DKIM in your DMARC policy.

Conclusion

SPF and DKIM alignment are essential parts of DMARC that strengthen email security by making sure only authorized sources can send emails on your behalf. By understanding and properly implementing alignment, you protect your domain from spoofing and enhance the overall trustworthiness of your email communications.

For more detailed steps on setting up SPF, DKIM, and DMARC for your domain, please see our related articles on each topic.