How to understand and resolve a DKIM permerror (no key for signature) in email headers?
Matthew Whittaker
Co-founder & CTO, Suped
Published 11 Aug 2025
Updated 18 Aug 2025
8 min read
Encountering a "dkim=permerror (no key for signature)" message in your email headers can be concerning, especially when your email service provider (ESP) suggests it's a temporary DNS issue with no impact on deliverability. From my experience, this assessment is often incorrect. A permerror, or permanent error, typically indicates a fundamental problem with your DomainKeys Identified Mail (DKIM) setup that actively prevents mail servers from verifying your email's authenticity.
This error means that the receiving mail server attempted to look up your DKIM public key in your domain's DNS records, but it couldn't find the necessary key to validate the email's signature. When this happens, it's a clear signal that your emails are failing DKIM authentication, which can severely impact your email deliverability, often leading to messages being sent directly to the spam or junk folder. It's a critical issue that requires immediate attention, as unauthenticated emails are frequently flagged as suspicious by major mailbox providers, including Gmail and Outlook. It's not a temporary glitch, but rather a configuration flaw that needs to be properly addressed at the DNS level.
Understanding DKIM and the 'No Key for Signature' error
DKIM is an email authentication standard that helps protect your domain from spoofing and phishing by adding a digital signature to your outgoing emails. This signature is created using a private key, which is kept secret by your sending server. When an email arrives at a recipient's server, that server uses a corresponding public key, which you publish in your domain's DNS records, to verify the signature. If the public key found matches the private key used to sign the email, the email is considered authentic.
The "no key for signature" aspect of the permerror is precise. It means the receiving server could not locate any DKIM public key in your DNS records for the specific selector and domain indicated in the email's DKIM-Signature header. This is distinct from a temperror, which implies a temporary issue that might resolve itself, such as a transient DNS lookup failure. A permerror indicates a permanent, unrecoverable problem that requires a manual fix on your part. For instance, if your email states dkim=fail (no key for signature) it suggests that the DNS record is simply not there, or is malformed, as noted by Microsoft's troubleshooting guides.
Without a valid DKIM signature, your emails are more likely to be treated as suspicious. This can lead to them being quarantined, rejected, or placed in the spam folder, directly impacting your email deliverability and sender reputation. It's crucial to address this promptly to ensure your legitimate emails reach their intended inboxes.
How to diagnose a DKIM 'no key' permerror
The first step to resolving this issue is to accurately diagnose it. You'll need to examine the full email headers of a message that received the "dkim=permerror (no key for signature)" status. Look for the DKIM-Signature header. Within this header, you'll find two crucial tags: s= (the selector) and d= (the signing domain).
Once you have these values, you can use an online DKIM authentication checker. Enter your selector (s=) and domain (d=) into the tool. This will perform a DNS lookup to see if your public key is correctly published and accessible. If the tool reports that no key is found, it confirms the permerror is indeed due to a missing or inaccessible public key. For further troubleshooting, you can refer to our guide on troubleshooting DKIM implementation issues.
It's important to distinguish this from other DKIM failures, such as a bad sig (bad signature) error, which indicates the key was found but the signature itself failed verification, often due to message modification or an incorrect private key. The "no key for signature" means the first step of verification (finding the key) has already failed.
Common causes and their resolutions
The primary cause of a "no key for signature" permerror is a missing or improperly configured DKIM public key in your domain's DNS records. This record, typically a TXT record, tells receiving mail servers where to find your public key. Without it, or if it's incorrect, they can't verify your email's authenticity, leading to authentication failure. For more insights into specific key errors, read about invalid RSA public key errors.
Other reasons might include typographical errors in the DNS record itself, such as incorrect characters, missing parts of the key, or improper formatting. Even a slight mistake can render the record unreadable to mail servers. Additionally, sometimes the selector (s=) or domain (d=) specified in your email's DKIM-Signature header might not match the one published in your DNS, leading to a lookup failure.
While DKIM permerrors are usually permanent, there's a slight nuance regarding DNS propagation. When you first publish a DKIM record, it takes time for these changes to update across the internet's DNS servers. During this propagation period, some mail servers might temporarily report a "no key for signature" error. However, this is distinct from a persistent, fundamental misconfiguration. Once propagation is complete, if the error persists, it points to a deeper setup issue. Understanding what to do when DKIM records are configured but unsigned is essential.
Common causes
Missing DNS record: The DKIM public key TXT record was never published in your domain's DNS.
Typo or format error: The published DNS record has a syntax error, extra spaces, or is malformed.
Incorrect selector or domain: The s= or d= values in the email header do not match your DNS record.
Resolutions
Publish the record: Obtain the correct DKIM TXT record from your ESP and add it to your DNS.
Correct the record: Double-check the DNS entry for any errors and ensure it matches the key provided by your ESP.
Align values: Ensure your sending system uses the correct selector and domain for signing that corresponds to your DNS entry.
Steps to resolve the DKIM permerror
Resolving a DKIM "no key for signature" permerror involves a few critical steps. The good news is that it's a fixable issue, though it requires access to your domain's DNS settings. Here’s how you can approach it:
Step 1: Obtain the correct public key
Your first action is to get the exact DKIM public key from your email service provider or the administrator of your mail server. This is typically a long string of characters that needs to be published as a TXT record in your DNS. They should also provide you with the correct selector (e.g., selector1._domainkey) for that key. If you are struggling with this, refer to our guide on common DKIM selectors.
Step 2: Access your DNS management
Log in to your domain registrar's website or your DNS hosting provider's control panel. This is where you manage your domain's DNS records (like A, MX, CNAME, and TXT records).
Step 3: Create or update the TXT record
Add a new TXT record or modify an existing one. The host (or name) for this record will typically be [selector]._domainkey, where [selector] is the specific selector your ESP provided. The value of the TXT record will be the public key itself, often starting with v=DKIM1; followed by the key data. Ensure there are no extra spaces or line breaks when copying the key.
After saving the DNS record, allow some time for DNS propagation to occur. This can take anywhere from a few minutes to several hours, depending on your DNS provider. Once sufficient time has passed, send test emails to various providers (e.g., Yahoo, AOL, Mail.com, etc.) and check the email headers again to confirm that the DKIM authentication now passes successfully.
Ensuring your email authenticity
Fixing a "no key for signature" permerror is a critical step towards maintaining a healthy email sending reputation and ensuring your messages land in the inbox, not the spam folder. Remember, this is a permanent issue that requires direct intervention. Proactive monitoring of your email authentication status through tools like DMARC monitoring and blocklist monitoring can help you catch these issues early and prevent significant deliverability problems. Regularly verifying your DNS records and working closely with your ESP to ensure proper configuration of your DKIM keys will protect your email program.
Views from the trenches
Best practices
Always obtain the precise DKIM public key and selector directly from your ESP or mail server administrator to avoid manual transcription errors.
Double-check your DNS TXT record for any hidden characters, extra spaces, or line breaks that can invalidate the key.
Utilize online DKIM lookup tools to verify the public key's accessibility and correctness in DNS after publication.
Implement DMARC with reporting to gain visibility into your DKIM authentication results and catch failures proactively.
Common pitfalls
Assuming a DKIM "permerror" is temporary and will resolve itself, leading to prolonged deliverability issues and reputation damage.
Copying and pasting the DKIM key from documentation without verifying its integrity, especially for multi-line records.
Not aligning the DKIM selector used by the sending system with the one published in DNS, causing lookup failures.
Overlooking the impact of DKIM authentication failures on sender reputation and inbox placement, leading to spam folder delivery.
Expert tips
Verify that your ESP has properly configured the private key on their sending infrastructure, as your public key is useless without it.
Ensure DNS propagation is complete after making changes by checking multiple DNS servers, not just one.
Set up alerts for DMARC reports so you're immediately notified if DKIM authentication begins to fail for your domain.
Consider key rotation best practices if your ESP supports it, enhancing security and potentially resolving long-standing issues.
Expert view
Expert from Email Geeks says you can test if the key is in DNS; if it is, then it's a temporary DNS error, but if it's not, it's a permanent issue.
2025-04-10 - Email Geeks
Expert view
Expert from Email Geeks says to find the selector, you need to examine the DKIM header for the 's=' and 'd=' values.
Gmail and 
Outlook. It's not a temporary glitch, but rather a configuration flaw that needs to be properly addressed at the DNS level.
Yahoo, 
AOL, 
Mail.com, etc.) and check the email headers again to confirm that the DKIM authentication now passes successfully.
