How to Fix DKIM=temperror (No Key for Signature) in Email Authentication


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The error dkim=temperror (no key for signature) occurs when the receiving mail server cannot find a valid DKIM public key to verify the email's signature. This typically happens when:

  • The DKIM record is missing from DNS
  • The selector (s= parameter) doesn't match any published key
  • DNS propagation hasn't completed

From your headers, we can see the critical DKIM information:

DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; 
d=holyfirepublishing.com; s=default; 
b=EXFzVKU0ZI0PBW6ug8u1mQ+D1 0WeVSF8lBoGNDKaM9o69wv9hkkedLn5Ga5hc6gaNGqjDtafv/DNv55Mo5t/a8Pqi48ciUBykHZl34 Hm98Zu4suFOK+MqMZIz9+Q7SZfgPdLRDtHLfyeLTRojxbeKSxJBZXTvvVT3N1Oy7PGQ0U1VR/WLe6 eTzli3cS7m6iI50CupM4cEPB0GY2eg1CRHAMk3lht4REa7WrsCeCJzDYqwCD8ojuo8ktQGbTtvKfB IsK+DBQT+W0c7GtICt1MvPp9UhLsb+bBvGAwWhzc8DARCW6N/I0EcOzqcV9Nujo3Y9Ch6eiDDeMYy qPPwf/elg==;

To check if your DKIM record exists, you can use this dig command:

dig +short txt default._domainkey.holyfirepublishing.com

Or for a more detailed query:

dig txt default._domainkey.holyfirepublishing.com

Here are the most likely fixes:

  1. Check your DNS records: 
    nslookup -type=txt default._domainkey.yourdomain.com
  2. Verify selector matches:
    The s=default in your DKIM-Signature must match the selector in your DNS record.
  3. Check DNS propagation:
    Use multiple DNS servers to verify your record has propagated globally.

Here's a Python script to verify your DKIM setup:

import dkim
import dns.resolver

def verify_dkim(domain, selector='default'):
    try:
        query = f"{selector}._domainkey.{domain}"
        answers = dns.resolver.resolve(query, 'TXT')
        for rdata in answers:
            print(f"DKIM record found: {rdata.strings}")
            return True
    except dns.resolver.NXDOMAIN:
        print(f"No DKIM record found for {query}")
    return False

verify_dkim('holyfirepublishing.com')

When troubleshooting, follow this sequence:

  1. Confirm the DKIM record exists in DNS
  2. Verify the selector name matches exactly
  3. Check the key format is correct
  4. Test with different email providers
  5. Use DKIM validation tools like MXToolbox

If you need to generate new DKIM keys, here's how:

openssl genrsa -out private.key 2048
openssl rsa -in private.key -pubout -out public.key

Then create your DNS TXT record with the public key.

  • DKIM record exists in DNS
  • Selector matches exactly
  • Key is properly formatted
  • DNS has fully propagated
  • Email server is signing outgoing messages

The error dkim=temperror (no key for signature) indicates that the receiving mail server couldn't find a valid DKIM public key to verify your email signature. This typically occurs when:

  • The selector (s= parameter) doesn't match your DNS records
  • The DNS record isn't properly propagated
  • The domain in the DKIM signature doesn't match your DNS records

From your email headers, we can see:

DKIM-Signature: v=1; a=rsa-sha256; d=holyfirepublishing.com; s=default;
...
ARC-Authentication-Results: dkim=temperror (no key for signature) header.i=@holyfirepublishing.com header.s=default

Key observations:

  • Your selector is set to 'default' (s=default)
  • The domain is holyfirepublishing.com
  • The server is trying to fetch the key from default._domainkey.holyfirepublishing.com

Here's how to properly configure DKIM for your setup:

# Example DNS TXT record for DKIM (you'll need to generate your own key)
default._domainkey.holyfirepublishing.com. IN TXT "v=DKIM1; k=rsa; p=MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA..."

For programmatic implementation in your web application:

// PHP example using PHPMailer with DKIM
$mail = new PHPMailer(true);
$mail->DKIM_domain = 'holyfirepublishing.com';
$mail->DKIM_private = 'path/to/your/private.key'; // Generated openssl key
$mail->DKIM_selector = 'default';
$mail->DKIM_passphrase = ''; // If your key has a passphrase
$mail->DKIM_identity = $mail->From;

After implementing the solution:

  1. Use online DKIM validators like dkimvalidator.com
  2. Check DNS propagation with dig or nslookup:
dig TXT default._domainkey.holyfirepublishing.com

Expected output should show your public key.

If you're still encountering issues:

  • Ensure your TTL is low when making DNS changes (300 seconds)
  • Verify key alignment between your signing domain and d= parameter
  • Check for DNS caching issues

For production systems, implement key rotation:

# Bash script to generate new DKIM keys
#!/bin/bash
openssl genrsa -out private.key 2048
openssl rsa -in private.key -pubout -out public.key

Remember to update both your DNS records and application configuration when rotating keys.