How to find DKIM record without selector?

Key findings

• Selector necessity: The DKIM selector is indispensable for looking up the public key in DNS. Without it, standard DNS checker tools cannot locate the record.
• Email headers: The most reliable method to find a DKIM selector is to examine the DKIM-Signature header of an email sent from the domain in question. The selector is typically indicated by the s= tag.
• Common selectors: Many email service providers (ESPs) use common, predictable selectors such as selector1, selector2, google, or default, which can be used for educated guesses.
• Automated scanning: Some specialized tools can automate the process of guessing common selectors and performing lookups against a database of known ESP selectors.

Key considerations

• Access to email source: If you can receive an email from the domain, checking the raw email headers is the most direct and accurate way to identify the selector. This is often the first step in troubleshooting DKIM implementation issues.
• DNS records structure: Understand that DKIM records are TXT records that require a specific hostname format, which always includes the selector. For more on the placement, see where SPF, DKIM, and DMARC records should be placed.
• Provider-specific selectors: Many email senders (like Google Workspace or Office 365) have standard selectors. Knowing the sending infrastructure can help narrow down guesses. DuoCircle provides a guide on how to find a DKIM selector by analyzing the DKIM signature in the header.

Key opinions

• Header analysis is key: The consensus among marketers is that inspecting email headers for the DKIM-Signature field (specifically the s= tag) is the most straightforward method if they can obtain an email from the target domain.
• Selector is essential for tools: Most DKIM lookup tools require a selector as input, making it difficult to proceed without this piece of information.
• Guessing is a valid strategy: Marketers often resort to guessing common selectors or using tools that try a list of standard selectors (e.g., default, s1, k1, google).

Key considerations

• Impact on deliverability: Proper DKIM alignment is crucial for email deliverability and DMARC compliance. Marketers understand that a missing or incorrect DKIM can lead to messages landing in spam folders. Understanding the basics of DMARC, SPF, and DKIM is foundational.
• Third-party services: When using an ESP, the selector is usually provided by the service. If it's not readily available, contacting their support is a common next step. Sometimes, services like Google Postmaster Tools can give insights, as discussed in the GoDMARC guide on finding DKIM selectors.
• Trial and error: Without a direct method, marketers may try a list of common selectors in lookup tools until a valid record is found. This is a pragmatic, albeit inefficient, approach.

Key opinions

• Technical requirement: Experts confirm that the selector is a mandatory part of the DNS query to locate the DKIM public key. There's no standard method to query for a DKIM record without a selector.
• Header inspection is primary: The most authoritative way to find the selector is by analyzing the DKIM-Signature header in a received email, as it explicitly includes the s= tag.
• Leveraging common ESP selectors: Knowing common selectors used by major ESPs (e.g., Office 365 uses selector1 and selector2; Google often uses google) can significantly aid in guessing the correct selector. For more common selector names, refer to a list of common DKIM selectors.
• Automated tools: Some specialized tools can automate the process of trying various common selectors until a valid DKIM record is found, streamlining the discovery process.

Key considerations

• MX record analysis: Experts suggest performing an MX lookup to identify the email service provider responsible for the domain, which can then help in predicting the likely DKIM selector. This is a common strategy in verifying DMARC, DKIM, and SPF setup.
• Selector rotation: While uncommon, some organizations rotate their DKIM selectors for security. This means a selector that worked yesterday might not work today, adding complexity to discovery. Read about how changing DKIM selectors impacts email reputation.
• DNS propagation: Even with the correct selector, DNS propagation delays can sometimes cause issues with immediate lookup results. Patience is key when dealing with DNS changes, as highlighted by SpamResource on general DNS troubleshooting.

Key findings

• RFC compliance: DKIM specifications, such as RFC 6376, define the selector as a tag within the DKIM-Signature header (the s= tag) that identifies the public key used to verify the signature.
• DNS record structure: The public key is stored in a TXT record at a specific hostname derived from the selector, followed by ._domainkey, and then the domain name (e.g., selector._domainkey.example.com). This structure makes the selector essential for lookup.
• No integrated validation tools: Platforms often note that they do not provide integrated DKIM validators, meaning external tools requiring the selector are necessary for verification, as highlighted by Zendesk support documentation.

Key considerations

• Purpose of selectors: Selectors allow a single sending domain to have multiple DKIM keys simultaneously, facilitating key rotation or the use of different keys for different purposes (e.g., transactional vs. marketing emails). NsLookup.io provides a practical guide to DKIM that explains this functionality.
• Implementation flexibility: While a selector is required for lookup, its naming convention is flexible, often chosen by the email service provider or administrator. This flexibility is why guessing without a received email can be challenging.
• Error messages: Documentation often explains that if a lookup tool reports no DKIM record found, it likely means the selector used was incorrect or the record hasn't propagated, not necessarily that DKIM isn't configured at all. This is discussed in how to fix DKIM from domain mismatch scenarios.