Summary
OpenDKIM wildcard configurations are generally supported and simplify management across multiple subdomains by using a single key. Documentation confirms their validity, while marketers emphasize the ease of managing fewer records. However, experts and marketers caution that this approach centralizes risk; a compromised key affects all subdomains. Proper implementation requires including the asterisk in both DNS and OpenDKIM configuration. Regular monitoring, key rotation, strong keys, and testing are recommended. While not directly about wildcard, other experts notes that other methods using single keys exist and basic deliverability practices still apply.
Key findings
- Validity & Support: Wildcard configurations are valid and supported by OpenDKIM and other platforms.
- Simplified Management: Wildcards reduce administrative overhead by using one key for numerous subdomains.
- Centralized Security Risk: A compromised key affects all subdomains under the wildcard, which is the most prominent risk.
- Implementation Requirement: The asterisk must be correctly configured in both DNS and OpenDKIM.
Key considerations
- Security Implications: Carefully weigh the risk of centralized key compromise.
- Monitoring and Auditing: Implement regular monitoring and auditing to detect unauthorized use.
- Key Rotation: Regularly rotate DKIM keys.
- Key Length: Use strong key lengths.
- Testing: Test the configuration with a subset of subdomains before global deployment.
- Configuration Alternatives: Consider methods to sign with a single DKIM key if wildcard is unsuitable.
- Email Basics: Remember core email security standards still apply.
What email marketers say
7 marketer opinions
The consensus is that OpenDKIM wildcard configurations *can* work, offering simplified DKIM management across multiple subdomains. However, proper implementation, monitoring, and security considerations are crucial. You must include the asterisk in both the DNS record and the OpenDKIM configuration. While it reduces administrative overhead, it also centralizes security risks.
Key opinions
- Feasibility: Wildcard DKIM configurations *can* work when properly implemented.
- Simplification: Wildcards reduce administrative overhead by allowing a single key for multiple subdomains.
- Security Impact: Compromising one subdomain key compromises all subdomains using the wildcard.
- Monitoring Importance: Regular monitoring is vital to detect unauthorized use.
Key considerations
- Implementation: Ensure asterisks are correctly used in both DNS and OpenDKIM configurations.
- Risk Assessment: Weigh the convenience of wildcard DKIM against the centralized security risk.
- Key Security: Employ robust key management practices, including strong key lengths.
- Testing: Test with a limited set of subdomains before global implementation.
- Key Rotation: Regularly rotate DKIM keys to minimize potential damage from compromise.
Marketer view
Email marketer from Super User responds that using a single DKIM key for all subdomains with a wildcard is viable but advises caution. If one subdomain is compromised, the DKIM key is compromised for all subdomains.
9 Oct 2022 - Super User
Marketer view
Email marketer from Reddit suggests that wildcard DKIM records are generally acceptable but recommends monitoring to ensure no unauthorized use occurs. Regularly auditing DKIM keys and configurations is important.
30 Jan 2025 - Reddit
What the experts say
3 expert opinions
Experts provide mixed perspectives. One suggests wildcards *might* work but highlights the potential for over-signing. Another offers using a single key for all domains as an alternative to KeyTable configurations (though not directly addressing wildcard functionality). The third emphasizes DKIM's general importance for inbox placement, rather than specifically addressing wildcard usage.
Key opinions
- Wildcard Uncertainty: Wildcard configurations *might* function but could lead to unintended signing behavior.
- Alternative Configuration: Using a single key across domains is presented as a potential alternative, though not equivalent, approach.
- DKIM Importance: DKIM setup is fundamentally important for email deliverability, regardless of wildcard usage.
Key considerations
- Over-signing: Consider the potential for wildcard configurations to attempt signing all passing domains.
- Configuration Options: Explore alternative DKIM configurations if wildcard behavior is undesirable.
- Deliverability Basics: Ensure proper DKIM setup is a core component of your email deliverability strategy.
Expert view
Expert from Spam Resource explains that while not directly answering about wildcard use, using a single key across multiple domains is a possible alternative to using KeyTable configurations.
1 Oct 2021 - Spam Resource
Expert view
Expert from Word to the Wise explains the importance of DKIM setup, but only states this in the context of ensuring that you pass spam filters and land in the Inbox.
28 Apr 2024 - Word to the Wise
What the documentation says
6 technical articles
Documentation across various sources confirms that OpenDKIM wildcard configurations are valid and simplify DKIM management for multiple subdomains. Wildcard selectors in the KeyTable match any selector under the specified subdomain. However, proper permissions, key management, and general security best practices remain crucial regardless of wildcard usage. The DKIM RFC provides foundational understanding of DKIM, enabling informed wildcard implementation.
Key findings
- Validity: OpenDKIM supports wildcard selectors in KeyTable files.
- Simplification: Wildcards streamline DKIM configuration for numerous subdomains.
- Security Neutrality: Wildcard use does not inherently impact security; proper practices are key.
- DKIM RFC relevance: Understanding of the DKIM RFC is valuable for proper implementation
Key considerations
- Permissions: Ensure appropriate permissions are set for keys and configurations.
- Key Management: Maintain robust key management practices.
- Security Practices: Adhere to general security best practices for DKIM.
- RFC Foundation: Understand the DKIM RFC to ensure a correct implementation.
Technical article
Documentation from Ubuntu Forums notes that wildcard usage in the KeyTable (e.g., `mail._domainkey.*`) is valid and matches any selector. This simplifies the signing process for multiple subdomains using a single key.
24 Apr 2023 - Ubuntu Forums
Technical article
Documentation from Oracle explains the process required to configure the DNS and KeyTable records for DKIM using a single DKIM key and wildcard, this simplifies the setup process for subdomains.
20 May 2023 - Oracle
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