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Why are my authenticated emails to Gmail soft bouncing with a DKIM and SPF fail error?

11 Marketer opinions3 Expert opinions5 Technical articles1 Resource

Summary

Authenticated emails soft bouncing with SPF and DKIM failures in Gmail indicates various potential issues. These include improper SPF and DKIM configuration, such as incorrect syntax, weak DKIM keys, DNS propagation delays, exceeding DNS lookup limits, and unauthorized 5321.From addresses. Using multiple email sending services without proper configuration, aggressive Gmail filtering, DMARC policies set to reject/quarantine, and email forwarding also contribute. Checking authentication records, analyzing bounce messages, maintaining a good sender reputation, and DKIM key rotation are essential for troubleshooting and resolving these deliverability problems.

Key findings

  • Incorrect Authentication Configuration: Improperly configured SPF and DKIM records are primary causes, including syntax errors, weak keys, missing IP addresses, and lack of DKIM key publishing.
  • DNS Propagation Issues: DNS propagation delays, DNS hosting issues, or problems transferring records can lead to intermittent authentication failures.
  • DMARC Policy Enforcement: DMARC policies set to reject or quarantine failing emails will cause Gmail to block or send them to spam.
  • SPF Lookup Limits Exceeded: Exceeding the SPF DNS lookup limit of 10 can result in SPF failures.
  • Multiple Sending Services: Using multiple sending services requires proper configuration in SPF to include all IPs/domains and separate DKIM keys for each.
  • Sender Reputation Impact: Gmail aggressively filters mail, making sender reputation and IP address health critical for deliverability.
  • 5321.From Authorization: If the 5321.From address is not authorized or aligned with the DKIM signing domain, DMARC can fail.
  • Email Forwarding: Email forwarding often causes SPF failures because the forwarding server isn't authorized.

Key considerations

  • Validate DNS Records: Regularly validate SPF, DKIM, and DMARC records for correct syntax and proper setup.
  • Monitor DMARC Reports: Monitor DMARC reports to identify authentication failures and adjust configurations.
  • Analyze Bounce Messages: Thoroughly analyze bounce messages from Gmail for specific reasons for failures.
  • Limit SPF Lookups: Keep SPF records below the 10 DNS lookup limit. Use mechanisms like 'include:' sparingly.
  • Rotate DKIM Keys: Implement a regular DKIM key rotation schedule to enhance security.
  • Address DNS Issues: Check for and resolve any client-side DNS hosting issues or migration problems affecting DNS record propagation.
  • Review Sending Infrastructure: Ensure that the sending infrastructure (mail servers, ESPs) are configured correctly and not blacklisted.
  • Confirm Authentication Visibility: Ensure authentication is visible to recipient servers by correctly publishing DKIM keys in DNS.

What email marketers say
11Marketer opinions

Authenticated emails soft bouncing with SPF and DKIM failures at Gmail can stem from several issues. Common causes include incorrect or missing SPF/DKIM records, DNS propagation delays, exceeding DNS lookup limits, and using multiple email sending services without proper configuration. DMARC policies set to reject or quarantine failing emails, email forwarding, and issues with DNS hosting or record migration also contribute to deliverability problems. Analyzing bounce messages and using tools to check the validity of authentication records are crucial for diagnosing and resolving these issues.

Key opinions

  • Authentication Configuration: Missing or incorrectly configured SPF and DKIM records are primary reasons for authentication failures. Ensure proper setup and syntax.
  • DNS Issues: DNS propagation delays, hosting issues, or migration problems can cause intermittent authentication failures. Verify DNS records are correctly propagated globally.
  • Multiple Sending Services: Using multiple email sending services requires careful configuration of SPF and DKIM to include all authorized IPs/domains and DKIM keys.
  • DMARC Policy: DMARC policies set to 'reject' or 'quarantine' can cause emails failing authentication to be blocked or sent to spam. Monitor DMARC reports.
  • Email Forwarding: Email forwarding can cause SPF failures if the forwarding server is not authorized in the sender's SPF record.
  • DKIM Key Problems: DKIM keys not published, or algorithms or key sizes that are too weak can cause DKIM to fail.

Key considerations

  • Record Validation: Regularly validate SPF, DKIM, and DMARC records using available tools to identify and correct any syntax errors or other issues.
  • Bounce Message Analysis: Thoroughly analyze bounce messages from Gmail to understand the specific reasons for authentication failures.
  • DNS Lookup Limits: Ensure that your SPF record does not exceed the limit of 10 DNS lookups to avoid authentication failures.
  • 5321.From Authorization: Ensure the 5321.From address is properly authorized to send emails to comply with DMARC requirements.
  • Client DNS Checks: If you manage client's DNS, ensure their records are properly configured. Ensure DNS hosting is reliable.
Marketer view

Email marketer from EmailonAcid suggests thoroughly analyzing the bounce messages from Gmail. These messages often contain specific details about why the email failed authentication, which can help pinpoint the issue.

August 2024 - Email on Acid
Marketer view

Email marketer from Super User forum notes that sometimes, the DNS records haven't fully propagated across the internet, causing intermittent SPF/DKIM failures. Using a DNS propagation checker can help confirm if the records are visible globally.

March 2024 - Super User
Marketer view

Email marketer from Email Geeks suggests the bounce message indicates DKIM and SPF weren't even present in the message headers. It could also be an issue with the client's DNS hosting or a migration issue where DNS records were not properly transferred.

January 2022 - Email Geeks
Marketer view

Email marketer from Reddit mentions email forwarding as a common cause for SPF failures. When an email is forwarded, the original SPF check might fail because the forwarding server isn't authorized in the sender's SPF record.

February 2022 - Reddit
Marketer view

Email marketer from Email Geeks says you can sign with DKIM, but if the key is not published, it is not effective.

October 2022 - Email Geeks
Marketer view

Email marketer from SendGrid explains that if a DMARC policy is set to 'reject' or 'quarantine', and emails fail SPF/DKIM checks, Gmail will reject or send them to spam, leading to soft bounces. You should monitor DMARC reports to identify authentication failures and adjust your configuration.

June 2021 - SendGrid
Marketer view

Email marketer from Email Geeks states that the authentication issue likely means the 5321.From is not authorized either.

December 2022 - Email Geeks
Marketer view

Email marketer from MXToolbox recommends using their tools to check the validity of your SPF, DKIM, and DMARC records. These tools can identify syntax errors or other issues that might cause authentication failures.

May 2021 - MXToolbox
Marketer view

Email marketer from Mailjet explains that SPF and DKIM failures can lead to deliverability issues, including soft bounces. The article recommends checking SPF records for accuracy and DKIM signatures for proper implementation.

February 2023 - Mailjet
Marketer view

Email marketer from Reddit shares that a common cause for SPF failure is exceeding the DNS lookup limit, or having multiple SPF records. Ensure that your SPF record includes all sending sources and stays within the limit of 10 DNS lookups.

November 2022 - Reddit
Marketer view

Email marketer from Stack Overflow explains that if using multiple email sending services, it's crucial to include all of their IPs/domains in your SPF record. For DKIM, each service should sign emails with their own DKIM key, and the DNS record for each should be configured.

December 2023 - Stack Overflow

What the experts say
3Expert opinions

Authenticated emails soft bouncing at Gmail, despite authentication, indicates potential issues with SPF and DKIM. The core advice emphasizes ensuring emails are genuinely authenticated, which requires verifying the sending domain, maintaining a good sender reputation, and ensuring authentication records are correctly configured and visible to email filters. Tools can assist in validating these records.

Key opinions

  • Authentication Visibility: Authentication must be visible and valid for filters to properly assess the legitimacy of the email. This requires proper DNS record configuration.
  • Sending Domain Verification: The sending domain's authentication needs to be checked; DKIM and SPF must pass for the specific domain used for sending.
  • Sender Reputation: Gmail's aggressive filtering requires monitoring and maintenance of sender reputation and IP address health.

Key considerations

  • Domain Verification: Ensure the domain used for sending emails is properly authenticated with both SPF and DKIM.
  • Reputation Monitoring: Actively monitor sender reputation and IP address health to avoid being flagged as a spam source.
  • Record Validation: Regularly validate authentication records (SPF, DKIM, DMARC) using available tools.
  • Review Bounce Messages: Thoroughly analyze bounce messages. Although not directly mentioned in the given answers, it's an implied next step for diagnostics.
Expert view

Expert from Word to the Wise (Laura Belgray) shares that Gmail is aggressively filtering mail and recommends to check your sender reputation and IP addresses. The article explains that you can also check authentication records and that they are valid using tools.

January 2022 - Word to the Wise
Expert view

Expert from Email Geeks asks what domain the user is sending from, noting the error indicates a lack of email authentication and stating "The sender must authenticate with at least one of SPF or DKIM. For this message DKIM checks did not pass and SPF check for [*.**.com] did not pass with ip: [*.*.*.*]."

November 2021 - Email Geeks
Expert view

Expert from Spam Resource explains that you need to ensure your authentication is visible so that filters can validate it. This means checking DNS records, proper syntax, and if you are using DMARC that is configured correctly.

August 2023 - Spam Resource

What the documentation says
5Technical articles

Authenticated emails soft bouncing with SPF and DKIM failures at Gmail often results from improper implementation of email authentication protocols. Key factors include incorrect SPF record syntax, weak DKIM keys or unsupported algorithms, and failure to include all sending IP addresses in the SPF record. In addition, regular DKIM key rotation is crucial for security and can impact deliverability. Following official guidelines and specifications is vital for proper setup.

Key findings

  • Authentication Required: Gmail requires SPF or DKIM authentication for proper delivery; failure to authenticate leads to deliverability issues.
  • SPF Syntax: Incorrect syntax in SPF records can cause authentication failures. Refer to RFC specifications for correct syntax.
  • DKIM Key Strength: Weak DKIM keys or unsupported algorithms result in authentication failure. Use a key size of at least 2048 bits and a supported algorithm like RSA-SHA256.
  • Complete SPF Records: SPF records must include all IP addresses of mail servers sending email on behalf of the domain.
  • DKIM Key Rotation: Regular DKIM key rotation enhances security and prevents deliverability problems associated with static keys.

Key considerations

  • Follow Guidelines: Adhere to the official documentation from Google, RFC, DKIM.org, Microsoft, and AuthSMTP for accurate configuration.
  • Syntax Validation: Validate SPF record syntax to avoid errors leading to authentication failures.
  • Algorithm Support: Ensure the DKIM algorithm used is supported by Gmail and other receiving mail servers.
  • Key Rotation Schedule: Implement a regular DKIM key rotation schedule to maintain strong security and deliverability.
  • Comprehensive IP Inclusion: Regularly review and update SPF records to ensure all authorized sending IP addresses are included.
Technical article

Documentation from RFC specifies SPF record syntax and usage. Incorrect syntax in an SPF record can cause it to fail during authentication, leading to deliverability problems.

March 2022 - RFC
Technical article

Documentation from AuthSMTP outlines the benefits of DKIM Key Rotation and how it can help prevent spoofing and phishing attacks. They also point out that not rotating keys can lead to deliverability issues down the line.

November 2024 - AuthSMTP
Technical article

Documentation from Google Support explains that to ensure proper delivery to Gmail, senders must authenticate their emails using SPF or DKIM. The documentation outlines the steps to set up these authentication methods.

January 2023 - Google Support
Technical article

Documentation from DKIM.org explains that a weak DKIM key or an unsupported algorithm can cause DKIM authentication to fail. It is recommended to use a key size of at least 2048 bits and a supported algorithm like RSA-SHA256.

November 2021 - DKIM.org
Technical article

Documentation from Microsoft outlines the importance of having correct DNS records for your domain. It indicates that an SPF record should include the IP addresses of all mail servers sending email on behalf of your domain.

February 2022 - Microsoft Documentation

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