Introduction to DKIM: Enhancing Your Email Security

Imagine sending a sealed letter with a seal that guarantees its authenticity and integrity from sender to recipient. That’s precisely what DKIM (DomainKeys Identified Mail) does for your emails. By attaching a digital signature to your messages, DKIM ensures that they remain untampered and verified, reinforcing trust and security in your business communications. In this article, we'll explore what DKIM is and how you can implement it to safeguard your emails effectively.

What is DKIM?

DKIM acts like a tamper-evident seal on your emails. It attaches a unique digital signature to the header of each email. When the email reaches its recipient, the receiving server uses this signature to verify that the email was indeed sent from your domain and hasn’t been altered during transit. This verification process ensures that your emails are both authentic and intact, bolstering the security and trustworthiness of your communications.

Technical Details of DKIM

DKIM uses a pair of digital keys, similar to a padlock and its combination. The first part of the digital key is the public key, which acts like the padlock on a door that everyone can see and use to verify the lock. The second part of the digital key is the private key, which acts as the combination needed to open the lock. Much like a lock’s combination, the private key is kept secret and stored securely on your email system. This ensures that only authorized emails are signed.

There are three main parts to DKIM:

1. Generating Keys: These are the keys that we described above. The public key is posted in your public DNS and the private key is posted on your email system.
2. Signing Emails: When you send an email, it’s 'locked' with your private key. This signature doesn’t encrypt the email but ensures it can be verified as legitimately sent by your domain.
3. Verifying Signatures: The receiving email system uses the public key from your DNS records to "unlock" the signature. If the key matches the lock, it confirms the email’s authenticity and integrity, ensuring it was sent from your domain and hasn't been tampered with.
   

Setting up DKIM

Implementing DKIM is a fairly straightforward process. However, it varies depending on what email system or email filtering service you are using. Configuring DKIM for every mail system is outside the scope of this article. Get in touch with us if you need assistance with your specific email system.

1. Generate the DKIM keys
• Your email system will have a way to generate the DKIM keys. It will provide a public key for you to setup in your public DNS, and it will store the private key. Typically, there will be two keys, or selectors, that are generated. These keys are complex, but don’t be intimidated by their contents.
2. Publish the Public Key
• You will need to create a TXT record in your public DNS with the two selector records. Some email systems will host these records for you (Microsoft 365 for example) and you only need to create a CNAME that points to their hosted record. Regardless the values are similar. Below is an example TXT record, remember there are typically two selectors.
  
  Name: selector1._domainkey
  Value: v=DKIM1; k=rsa; p=MIIBIjANBgkqhkiG9w0BAQEFAAOC...
  
  Name: selector2._domainkey
  Value: v=DKIM1; k=rsa; p=MIIBIjANBgkqhkiG9w0BAQEFAAOC...
3. Test the Records
• Once your records are published, use an online checking tool to make sure that both records are set properly. We recommend MXToolbox's DKIM tool for this task. Place your domain in the first box, and then "selector1" or "selector2" in the second box.

New DKIM records usually start working 5-10 minutes after publishing. If you are using M365 and cannot get the Selector2 record to appear, try rotating your DKIM keys in the M365 Defender portal; this will typically resolve the issue. Changes to existing DKIM records can take up to 48 hours to propagate.

4. Configure your Mail Server
• Ensure that your email server is configured to use the private key when sending emails. This process varies depending on your email system, so it's best to follow the specific documentation provided by your provider. Some configurations are very simple; for example, in Microsoft 365, you just need to toggle a slider to start using DKIM.

Challenges and Best Practices

Managing DKIM keys can be daunting, especially when it comes to rotating keys regularly to maintain security. Additionally, configuring DKIM varies depending on your email service provider, which can add to the complexity. You might encounter difficulties ensuring that all your email sources are properly aligned with your DKIM setup, especially if you use multiple third-party services.

However, these challenges are manageable with some best practices. Regularly updating your DKIM keys is crucial to maintaining their security, much like changing passwords periodically. We recommend that you rotate your DKIM keys every 6 to 12 months. It's also important to test your DKIM configuration periodically using tools like MXToolbox to catch any issues early.

Combining DKIM with other email authentication protocols like SPF and DMARC provides a comprehensive security strategy, significantly enhancing the protection of your communications. Think of it as maintaining a high-tech security system that, with a little regular upkeep, keeps your digital communications fortress secure.

Secure Your Emails with a Free Consultation!

Take control of your email security today by implementing DKIM. Protect your communications from tampering and build trust with your recipients. If you need assistance with setting up DKIM or have any questions, our IT experts offer a free consultation to help you get started. Contact us to ensure your emails are authenticated and secure, and take the first step toward a more secure digital presence. Don’t wait—strengthen your email security now with a free consultation!