In the realm of email security, DMARC plays a pivotal role by leveraging two existing email authentication methods: SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail). To understand how DMARC improves email security, it’s essential to grasp what SPF and DKIM alignment mean.
What is SPF?
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 allows the receiver to check that an email was indeed sent and authorized by the owner of that domain. It works by affixing a digital signature, linked to a domain name, to each outgoing email message. This signature can be verified by the recipient to ensure the email has not been altered in 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 consider an email as authenticated, the email must pass either the SPF or DKIM check, and the domain in these checks must align with the domain in the "From" address. Alignment ensures that the domains match or are a subdomain, providing an additional layer of security.
There are two types of alignment: strict and relaxed.
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.
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 crucial because it prevents attackers from spoofing email addresses from your domain. Without alignment, an attacker could pass SPF or DKIM checks using their own domain, making the email look legitimate. By enforcing alignment, DMARC ensures that only authorized servers can send emails on behalf of your domain.
Implementing SPF and DKIM Alignment
Configure SPF Records:
Publish an SPF record in your DNS settings specifying which mail servers are authorized to send emails on your behalf.
Ensure that the domains used in the SPF record align with the domain in the "From" address.
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.
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 fundamental components of DMARC that enhance email security by ensuring that only legitimate sources can send emails from your domain. By understanding and implementing proper alignment, you protect your domain from spoofing and improve the overall integrity of your email communications.
For more detailed steps on configuring SPF, DKIM, and DMARC for your domain, please refer to our related articles on each topic.
