Understanding SPF and DKIM to Improve Email Deliverability

The importance of email security is well understood in 2021. Huge organizations and brands highly benefit from securing their emails. A huge part of email security and deliverability are email protocols like SPF and DKIM. These terms get thrown out a lot, but today, we’ll learn about SPF and DKIM in detail and how they help improve email deliverability.

What is SPF?

SPF or Sender Policy Framework (SPF) is an email authentication protocol that allows domain owners to specify which email servers are permitted to send email from their domain(s).

As an email is being delivered, SPF allows the recipient email server to verify whether the mail claiming to be from a specific sender is actually from an IP address that is authorized to send mail on the domain's behalf. This is possible as the DNS records for a domain publish a list of domains and IP addresses that are allowed to send emails on the domain's behalf.

What is DKIM?

DKIM or DomainKeys Identified Mail is an anti-tamper protocol that ensures your mail remains secure in transit. DKIM uses digital signatures to check that the email was sent by a specific domain.

DKIM uses two actions to validate your messages. The first action occurs on a server sending DKIM signed emails, while the second happens on a recipient server checking DKIM signatures on incoming messages. The entire process is made possible by a private and public key pair. The private key is kept secret and safe, either on your server or with your ESP. The public key is added to the DNS records of your domain to broadcast to the world to help verify emails. This is done by providing a digital signature for all emails sent by a server that has DKIM configured.

SPF and DKIM for Beginners

When email was introduced to the world, there were limited methods to check and verify the sender. Verifying where the email came from and who the sender was, is and always has been a tough process. SPF and DKIM protocols are used to verify and authenticate the sending sources and protect your inbox against spam and malicious email.

SPF Mechanism

SPF is used by the receiver to verify that an incoming email from a domain was sent from a host approved by the domain's administration. It is based on the well-known Domain Name System (DNS).

The following mechanism is employed:

• The domain admin describes the list of authorized senders with the help of an SPF record. An SPF record is a policy that is listed as part of the domain's overall DNS records.
• When an inbound mail server receives an email, it checks the DNS for prescribed bounce rules. The inbound server then compares the email sender's IP address to the list of approved IP addresses in the SPF record.
• The receiving mail server then decides whether to accept, deny, or otherwise flag the email.

DKIM Mechanism

DKIM adds a digital signature to the headers of an email message. That signature can be validated against a public cryptographic key in the organization’s DNS records. In other words, a public key is issued as a TXT record for the domain's DNS Manager in the DKIM process (registrar of the domain or DNS Provider).

Every outgoing email has its own signature that is generated using the domain's private key. This private-public key combination is used by the recipient email server to verify the email source. When an inbound mail server gets an email, it looks up the DNS records to find the sender's public DKIM key. This key is used by the inbound server to decrypt the signature and compare it to a newly computed version. The message can be proven to be valid and integrated during the transit if the two values match.

Conclusion

To secure your emails and prevent irreversible damage caused by cyber attacks like phishing, ransomware, data breaches, impersonation, etc. it is very important that protocols such as SPF and Dkim are implemented for your domain to verify incoming emails.

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