To ensure that your DKIM (DomainKeys Identified Mail) or DK (DomainKeys) signature is valid, you need to correctly configure your DKIM settings on your mail server and verify that the signatures are being correctly applied and recognized by the recipient servers. Here’s how you can do it:
Step 1: Generate DKIM Keys
Generate a DKIM Key Pair: Most mail servers or hosting providers offer tools to generate a DKIM key pair (public and private keys). If you’re managing your own server, you can use tools like openssl to generate these keys.
Public Key: This key will be published in your domain's DNS as a TXT record.
Private Key: This key will be used by your mail server to sign outgoing emails.
Step 2: Publish the DKIM Public Key in DNS
Create a TXT Record: In your DNS management interface, create a new TXT record.
Name/Host: The name should be in the format selector._domainkey.yourdomain.com, where selector is a name you choose (like default or mail).
Value/Content: The value should contain the public key, in this format:
v=DKIM1; k=rsa; p=your_public_key_here
v=DKIM1: Specifies the DKIM version.
k=rsa: Specifies the key type (RSA).
p=your_public_key_here: Replace with the actual public key.
Step 3: Configure Your Mail Server to Use DKIM
Enable DKIM Signing: Configure your mail server or email service provider to sign outgoing emails with the DKIM private key.
Set the Selector: Ensure that the selector name in your mail server configuration matches the selector used in your DNS record.
Test the Setup: Send a test email to ensure that the DKIM signature is being applied.
Step 4: Send a Test Email
Send to a Testing Service: Use a service like Mail-tester, MXToolbox DKIM Lookup, or Gmail to verify your DKIM signature.
Analyze Results: Check the headers of the received email to see if the DKIM signature is valid.
In Gmail, open the email, click the three dots next to the reply button, and select "Show original."
Look for the DKIM-Signature header and a line that says dkim=pass. If it says pass, the signature is valid.
Step 5: Verify DKIM Configuration
Check with MXToolbox: Use the MXToolbox DKIM tool to look up your DKIM record and verify that it's properly configured and visible.
Step 6: Check Email Headers
Inspect Headers: Look at the headers of a sent email to ensure the DKIM signature is present and correct.
DKIM-Signature Header: The header should look something like this:
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yourdomain.com; s=selector;
h=from:to:subject:date; bh=hash_value;
b=signature_value;
Validation: The receiving server should verify this signature against the public key in your DNS record. If the signature is valid, the email should pass DKIM validation.
Step 7: Monitor DKIM Performance
Regularly Review DKIM Reports: If you have set up DMARC, you'll receive reports that include DKIM validation results, helping you monitor the effectiveness of your DKIM setup.
Troubleshooting DKIM Issues
DNS Propagation: If you’ve just set up DKIM, give it time for DNS changes to propagate.
Mismatched Selectors: Ensure the selector in your mail server matches the one in your DNS record.
Correct Formatting: Double-check that there are no line breaks or spaces in the middle of your p= value (public key) in the DNS record.
By following these steps and regularly testing, you can ensure that your DKIM or DK signature is valid and properly securing your emails.
