Summary
Gmail DKIM domain rate limiting errors arise from various factors, primarily related to email authentication and sender reputation. Common causes include SPF and DKIM failures, DNS misconfigurations, poor list hygiene, being on email blacklists, and failing to adhere to bulk email sender guidelines. The error message `421-4.7.28` indicates Gmail has detected an unusual rate of unsolicited mail from the DKIM domain. SPF and DKIM are complementary authentication methods, with SPF identifying authorized sending servers and DKIM ensuring message integrity, and DMARC relying on both to enforce email handling policies. Maintaining a clean email list, monitoring sender reputation, and correctly implementing SPF, DKIM, and DMARC are crucial for preventing deliverability issues and rate limiting. A connection between SPF and DKIM errors has been observed where blocking SPF senders has resolved DKIM bounce issues. Regularly checking DKIM records and performing SPF record lookups are also essential.
Key findings
- Error Message: The error message `421-4.7.28` signifies that Gmail has detected a high rate of unsolicited mail originating from the DKIM domain.
- SPF/DKIM Failure: Consistent failures in SPF and DKIM authentication processes are a primary cause of Gmail rate limiting.
- Sender Reputation: A poor sender reputation, often resulting from high bounce rates and spam complaints, can lead to rate limiting.
- SPF/DKIM Synergy: SPF and DKIM are complementary authentication methods; SPF identifies authorized mail servers, while DKIM ensures message integrity.
- DMARC Policy: DMARC leverages both SPF and DKIM results to enforce policies on how email receivers should handle unauthenticated messages.
- List Quality: Poor list hygiene (e.g., high bounce rates, unengaged subscribers) negatively impacts sender reputation and can trigger rate limits.
- Authentication Protocols: Proper configuration of SPF, DKIM, and DMARC is essential for email authentication and preventing spoofing and phishing attacks.
- DNS Issues: Incorrect or outdated SPF and DKIM records in DNS can cause authentication failures and rate limiting.
- Blacklisting: Being listed on email blacklists can significantly impact deliverability and increase the likelihood of rate limiting.
- Bulk Sender Guidelines: Failure to adhere to bulk email sender guidelines set by email providers (like Gmail and Microsoft) can lead to deliverability problems.
- SPF & DKIM relation: There is an observed relation between SPF and DKIM errors. By blocking SPF can stop DKIM errors.
Key considerations
- Implement Authentication: Implement and correctly configure SPF, DKIM, and DMARC to authenticate your emails.
- Maintain List Quality: Regularly clean your email list by removing inactive subscribers and addressing bounces to reduce spam complaints.
- Monitor Reputation: Monitor your sender reputation using tools like Google Postmaster Tools to identify and address potential issues.
- DNS Record Verification: Regularly verify the accuracy and completeness of your SPF and DKIM records in DNS.
- Follow Sender Guidelines: Adhere to bulk email sender guidelines provided by major email providers to avoid deliverability problems.
- Address Authentication Failures: Investigate and address the root causes of any SPF or DKIM authentication failures.
- Monitor Blacklists: Monitor your domain and IP addresses for listing on email blacklists and take steps to get removed if necessary.
- SPF Setup: Ensure SPF records accurately list all authorized sending servers.
- DKIM Implementation: Implement DKIM for improved handling of forwarded emails and resilience against SPF failures.
- DMARC Alignment: Understand DMARC alignment modes to properly configure handling of SPF and DKIM results.
- Review SPF Records: Review your SPF record and verify it's configured correctly. Use tools such as Ultratools.
- Email Blacklists: Regularly check your domain/IP address against known email blacklists. This can tell you if your email has been detected as spam and is causing rate limiting.
What email marketers say
15 marketer opinions
Gmail DKIM domain rate limiting errors are often linked to issues with email authentication, particularly SPF and DKIM. Encountering a `421-4.7.28` error indicates unusual unsolicited mail originating from your domain. Problems like SPF hard fails, DNS misconfigurations, and being on email blacklists can trigger these limits. A poor sender reputation, driven by high bounce rates, spam complaints, and unengaged subscribers, significantly contributes. Implementing SPF, DKIM, and DMARC correctly, maintaining a clean email list, and monitoring sender reputation are crucial to avoid these errors. A connection between SPF and DKIM errors has been observed, where blocking an SPF sender has stopped DKIM bounces.
Key opinions
- Error Message: The error message `421-4.7.28` indicates Gmail has detected an unusual rate of unsolicited mail from your DKIM domain.
- SPF/DKIM Failure: Consistent failure of SPF and/or DKIM authentication can lead to Gmail rate limiting.
- Sender Reputation: A poor sender reputation, influenced by high bounce rates and spam complaints, can trigger rate limits.
- SPF & DKIM relation: There is an observed relation between SPF and DKIM errors. By blocking SPF can stop DKIM errors.
- Authentication Protocols: SPF and DKIM are essential for email authentication; when configured incorrectly, they can lead to deliverability issues.
- DNS Issues: DNS misconfigurations in SPF and DKIM records can lead to authentication failures.
- Blacklisting: Being listed on email blacklists increases the likelihood of rate limiting.
Key considerations
- Implement Authentication: Implement SPF, DKIM, and DMARC protocols correctly to authenticate your emails.
- List Hygiene: Maintain a clean email list by removing inactive subscribers and managing bounces.
- Monitor Reputation: Regularly monitor your sender reputation using tools like Google Postmaster Tools.
- Review SPF Records: Review your SPF record and verify it's configured correctly. Use tools such as Ultratools.
- Email Blacklists: Regularly check your domain/IP address against known email blacklists. This can tell you if your email has been detected as spam and is causing rate limiting.
Marketer view
Email marketer from Sendinblue explains that SPF, DKIM, and DMARC are email authentication protocols that help improve email deliverability and protect your domain from spoofing and phishing attacks. Implementing these protocols can reduce the likelihood of your emails being marked as spam and improve your sender reputation.
3 May 2024 - Sendinblue
Marketer view
Marketer from Email Geeks reports receiving the same transient DKIM error with DKIM [ 15].
18 Dec 2023 - Email Geeks
What the experts say
3 expert opinions
SPF identifies authorized servers for a domain, flagging unauthorized senders as potential spam, but can be problematic with email forwarding. DKIM, while more complex, maintains validity through forwarding. DMARC uses both SPF and DKIM, focusing on the From: header's domain and alignment between authentication results.
Key opinions
- SPF Authorization: SPF designates authorized mail servers for a domain.
- Forwarding Issue: SPF can fail when emails are forwarded through unauthorized servers.
- DKIM Advantage: DKIM signatures remain valid during email forwarding.
- DMARC Dependency: DMARC requires both SPF and DKIM and focuses on the From: header domain.
Key considerations
- SPF Setup: Ensure SPF records accurately list all authorized sending servers.
- DKIM Implementation: Implement DKIM for improved handling of forwarded emails and resilience against SPF failures.
- DMARC Alignment: Understand DMARC alignment modes to properly configure handling of SPF and DKIM results.
Expert view
Expert from Word to the Wise explains that DMARC needs both SPF and DKIM, however DMARC only cares about the domain in the From: header. The alignment mode tells the receiver if the SPF and DKIM results need to match.
14 May 2022 - Word to the Wise
Expert view
Expert from Spam Resource explains that SPF is used to show which servers are permitted to send mail from a domain. If a server sends from a domain but isn't listed as permitted in the SPF, then this should be treated as spam. He also explains that it does not break forwarding.
26 Oct 2023 - Spam Resource
What the documentation says
5 technical articles
To avoid Gmail DKIM rate limiting, follow bulk sender guidelines, maintain good authentication practices (SPF, DKIM), manage spam rates, and offer clear unsubscribe options. Monitor sender reputation using tools like Postmaster Tools. SPF and DKIM work together to verify senders and message integrity, with DMARC building upon them to handle authentication failures through policy enforcement. Maintaining good list hygiene and addressing authentication issues are crucial for deliverability and preventing rate limiting, and regularly checking your DKIM record for errors.
Key findings
- Bulk Sender Guidelines: Following bulk sender guidelines is crucial for avoiding rate limiting.
- SPF/DKIM Synergy: SPF and DKIM are complementary authentication methods that enhance email deliverability.
- DMARC Policy: DMARC builds on SPF and DKIM by providing policies for handling authentication failures.
- List Hygiene Impact: Poor list hygiene can lead to deliverability problems and rate limiting.
- DKIM Record Errors: DKIM record errors, such as extra spaces or incorrect selectors, can cause authentication failures.
Key considerations
- Adhere to Guidelines: Adhere to bulk email sender guidelines to avoid deliverability issues.
- Implement Authentication: Implement and correctly configure SPF and DKIM for email authentication.
- DMARC Configuration: Implement DMARC to specify how receivers should handle authentication failures.
- Maintain List Quality: Practice good list hygiene by removing inactive subscribers and managing bounces.
- Monitor Reputation: Monitor sender reputation and authentication results using available tools.
- Verify DKIM Record: Regularly check your DKIM record for errors to ensure proper authentication.
Technical article
Documentation from Google Workspace Admin Help explains that to prevent Gmail from limiting your DKIM domain, ensure you are following bulk email senders guidelines, specifically related to authentication, spam rates, and clear unsubscribe options. They also suggest monitoring your sender reputation using Postmaster Tools.
8 Jan 2025 - Google Workspace Admin Help
Technical article
Documentation from RFC 7489 (DMARC standard) explains that DMARC builds upon SPF and DKIM by providing a policy that specifies how email receivers should handle messages that fail SPF and DKIM checks. DMARC allows domain owners to instruct receivers to reject, quarantine, or deliver emails that fail authentication, providing an additional layer of protection against email spoofing.
16 Aug 2022 - RFC 7489
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