Generate DKIM for Zimbra

How to Generate and Configure DKIM for Zimbra

Email authentication is a critical component of cybersecurity, ensuring that email messages originate from legitimate sources and have not been altered in transit. DomainKeys Identified Mail (DKIM) is a widely used authentication mechanism that helps email recipients verify the sender's authenticity by using cryptographic signatures.

If you are using Zimbra Mail Server, enabling DKIM is an essential step in strengthening your email security. This guide will walk you through setting up DKIM for Zimbra and ensuring its proper configuration.

What is DKIM and Why is it Important?

DKIM (DomainKeys Identified Mail) is an email authentication method that adds a digital signature to your outgoing email messages. The recipient’s email server then verifies this signature against the sender’s public key, ensuring that:

• The email has not been tampered with during transmission.
• The message genuinely originates from an authorized source.
• It improves deliverability by preventing emails from being marked as spam.

Steps to Set Up DKIM on Zimbra

Setting up DKIM signing in Zimbra involves two primary steps:

• Generating the DKIM Key on the Zimbra Server
• Adding the DKIM Record to Your Domain’s DNS

Let’s go through each step in detail:

Step 1: Generate DKIM Keys on the Zimbra Server

Log into your Zimbra MTA (Mail Transfer Agent) Server as the root user.

Execute the following command to generate a DKIM key for your domain:

/opt/zimbra/libexec/zmdkimkeyutil -a -d yourdomain.com

Replace yourdomain.com with your actual domain name.

After running the command, the system will generate a DKIM public key and display the output on the screen.

Copy the generated DKIM record carefully. You will need to publish it in your domain’s DNS settings.

Step 2: Add the DKIM Record to Your DNS

Now that you have the DKIM record, you need to add it to your domain’s DNS TXT record. Follow these steps:

• Log in to your DNS provider’s control panel (e.g., GoDaddy, Cloudflare, AWS Route 53, etc.).
• Navigate to the DNS Management section.
• Add a new TXT Record with the following details:

    Host Name: default._domainkey.yourdomain.com
    Record Type: TXT
    Value: Paste the public DKIM key you copied earlier.
    

Save the changes and allow up to 48-72 hours for the DNS to propagate.

Verifying DKIM Configuration

Method 1: Using Zimbra Commands

Run the following command to check if DKIM is enabled for your domain:

/opt/zimbra/libexec/zmdkimkeyutil -q -d yourdomain.com

If the key is properly configured, you should see the public key details displayed.

Method 2: Using Online DKIM Checkers

Use a free DKIM record lookup tool such as:

• MXToolbox DKIM Checker
• Google Admin Toolbox

Troubleshooting Common DKIM Issues

• DNS Record Not Found: Ensure that your TXT record is correctly formatted and DNS changes have propagated.
• Email DKIM Signatures Are Not Validated: Confirm DKIM signing is enabled on Zimbra using:

zmprov gs `zmhostname` | grep zimbraAmavisDomainSigningEnabled

It should return TRUE.

Enhancing Email Security: Use SPF, DKIM, and DMARC Together

While DKIM helps authenticate emails, it is only one piece of the email security puzzle. To fully protect your domain from email spoofing, phishing, and spam, you should also implement:

• SPF (Sender Policy Framework) – Defines authorized mail servers for sending emails on behalf of your domain.
• DMARC (Domain-based Message Authentication, Reporting, and Conformance) – Enforces email authentication policies.

Enable DMARC for Stronger Security

To set up DMARC, create a TXT record in your DNS with:

    Host: _dmarc.yourdomain.com  
    Type: TXT  
    Value: v=DMARC1; p=quarantine; rua=mailto:[email protected]; ruf=mailto:[email protected]
    

Conclusion

By setting up DKIM on Zimbra, you can ensure that your outgoing emails are authenticated and trusted by recipients. However, to fully protect your domain, combine DKIM, SPF, and DMARC for a comprehensive email security strategy.

Need Help?

If you need assistance with DKIM, DMARC, or email security, start your free DMARC trial today! 🚀