DomainKeys Identified Mail (DKIM) is a technology that allows email senders to associate a domain with a specific message, guaranteeing its authenticity and protecting against spoofing.
In the world of digital communication, where phishing attacks and spam are daily occurrences, DKIM plays a critical role in email correspondence security. This technology uses digital signatures to verify the origin and integrity of messages.
How does DKIM work?
DKIM works by "signing" the email with a digital signature - a special field that is added to the header of the message. The process involves several key steps:
1. Generating the signature
The Mail Transfer Agent (MTA) generates a unique signature using a cryptographic algorithm. This algorithm is applied to the content of the signed fields and creates a unique string of characters called a "hash value".
2. Storing the public key
After generating the signature, the public key used to create it is stored in the DNS records of the domain from which the email was sent.
3. Verification upon receipt
When the email is received, the recipient's MTA:
- Extracts the DKIM signature from the email header
- Takes the public key from the sending domain's DNS records
- Uses the key to decrypt the hash value in the header
- Simultaneously recalculates the hash value for the received email
- Compares the two values
If the two hash values match, it proves that the email has not been modified after being sent.
Advantages of DKIM
- Protection against email spoofing and phishing attacks
- Improved deliverability - fewer emails marked as spam
- Increased trust with recipients
- Protection of the domain's reputation
- Compatibility with other technologies (SPF, DMARC)
- Transparency when verifying authenticity
DKIM provides users with security that the email truly comes from the specified domain and that it has not been modified on its way.
— Email Security Standards
Does DKIM filter emails?
DKIM by itself does not filter emails. Instead, it provides valuable information to filters created by the receiving domain to make more informed decisions.
How does it affect filtering?
- Positive verification: If the email comes from a trusted domain and is successfully verified via DKIM, the spam score can be significantly reduced
- Failed verification: If the DKIM signature cannot be verified (because the email is spoofed or for another reason), the email may be:
- Marked as spam
- Placed in quarantine
- Receive a warning label in the subject line
Practical examples
Gmail, for example, does not deliver emails from eBay.com or PayPal.com if the DKIM signature cannot be successfully verified. This is due to the extremely high likelihood that such emails are phishing attacks.
Tips for implementation
When setting up DKIM for your email server, keep the following recommendations in mind:
- Use a sufficiently long cryptographic key (minimum 1024 bits, recommended 2048 bits)
- Rotate keys regularly for increased security
- Test the DKIM configuration before going into production
- Combine DKIM with SPF and DMARC for maximum protection
- Monitor DKIM statistics and reports regularly
Conclusion
DKIM is an extremely important technology for protecting email communication in the modern digital world. Although managing an email server can be a challenge and create various problems, implementing DKIM is a critical step for ensuring email deliverability and protection.
We hope this article has helped you understand how DKIM digital signatures work and why they are so important for email security. With proper configuration, DKIM significantly reduces the risk of phishing and improves your domain's reputation.
If you need help setting up DKIM or other email security technologies, the Creative Idea team can consult and assist you.
