How do I properly set up SPF and DKIM records for email marketing, including handling multiple SPF records, IP ranges, bounce capturing, and Google Postmaster Tools verification?

Summary

Proper email deliverability relies on correctly setting up SPF, DKIM, and DMARC records, along with careful management of IP ranges, bounce handling, and monitoring through Google Postmaster Tools. SPF authenticates sending sources, DKIM ensures message integrity, and DMARC defines how to handle authentication failures. Key considerations include using a single SPF record, precise IP range specifications, proper syntax for SPF, managing bounces, implementing DMARC, and continuous monitoring for changes and potential issues.

Key findings

  • SPF and DKIM Fundamentals: SPF verifies authorized sending IPs, and DKIM cryptographically signs emails to ensure message integrity.
  • SPF Record Configuration: Use a single, correctly formatted SPF record, avoiding multiple entries or broad IP ranges.
  • DKIM Implementation: DKIM uses a digital signature to ensure the email was sent by an authorised domain, and the content hasn't been altered during transit.
  • DMARC Policy: DMARC provides instructions to receiving mail servers on how to handle emails that fail SPF and DKIM checks.
  • Google Postmaster Tools: Google Postmaster Tools helps monitor sending reputation, spam rates, and other deliverability metrics.
  • Bounce Management: Proper bounce handling is essential for maintaining a good sender reputation.

Key considerations

  • Dynamic Infrastructure: Keep SPF records updated to reflect any changes in sending infrastructure.
  • Security and Forging: Avoid listing entire colo spaces in SPF records to mitigate forging risks.
  • Monitoring and Adaptation: Continuously monitor deliverability metrics and adapt authentication settings as needed.
  • DNS Lookup Limits: Be mindful of DNS lookup limits in SPF records and consider SPF flattening to avoid exceeding them.

What email marketers say
10Marketer opinions

Properly setting up SPF and DKIM records, along with DMARC, is crucial for email deliverability. The process involves creating TXT records in your domain's DNS settings to authorize sending mail servers, ensuring correct SPF syntax, handling bounce messages effectively, and monitoring email authentication metrics. Key steps include consolidating multiple SPF records into one, using 'include:' mechanisms appropriately, managing IP ranges carefully, and verifying setup with Google Postmaster Tools. Additionally, it's important to handle bounce messages promptly to maintain a good sending reputation and monitor authentication metrics for continuous optimization.

Key opinions

  • SPF Syntax: Use the correct syntax for combining SPF records and utilize 'include:' mechanisms properly. Avoid multiple SPF records; consolidate into one.
  • DKIM Signature: DKIM adds a digital signature, verifying the email's authenticity and ensuring content integrity during transit.
  • Bounce Handling: Properly handle bounces (hard and soft) to maintain sender reputation; implement a feedback loop.
  • IP Ranges: Manage IP ranges carefully and only include authorized IP addresses in your SPF record.
  • Google Postmaster Tools: Create a separate TXT record for Google Site Verification and use Google Postmaster Tools to monitor deliverability.
  • SPF flattening: Consider SPF flattening to prevent DNS lookup limits being exceeded.
  • DMARC Implementation: Implement DMARC for policy enforcement and to handle emails failing SPF and DKIM checks.

Key considerations

  • Infrastructure Changes: Update SPF records whenever sending infrastructure changes to avoid authentication failures.
  • Monitoring: Consistently monitor email authentication setup and deliverability metrics for continuous improvement.
  • Impact of Setup Errors: Incorrectly configured SPF records can impact deliverability and sender reputation.
Marketer view

Email marketer from Stack Overflow clarifies that the correct SPF syntax involves using 'include:' mechanisms to reference other domains' SPF records and that using 'ip4:' and 'ip6:' mechanisms should be limited to only the IP addresses that you directly control.

March 2023 - Stack Overflow
Marketer view

Email marketer from Sendinblue explains that DKIM adds a digital signature to your emails, verifying that the email was sent by the authorized domain and that the message content hasn't been altered during transit, thereby improving email deliverability.

May 2022 - Sendinblue
Marketer view

Email marketer from SparkPost shares that properly handling bounces (both hard and soft bounces) is crucial for maintaining a good sender reputation. Implementing a feedback loop and removing invalid email addresses from your list are essential.

April 2022 - SparkPost
Marketer view

Marketer from Email Geeks explains the correct syntax for combining SPF records, advising against separate `v=spf1` entries and suggesting a merged format. He also questions the use of a /18 IP range for email.

August 2022 - Email Geeks
Marketer view

Marketer from Email Geeks advises creating a separate TXT record for the `google-site-verification` value and retrying verification in Google Postmaster Tools if the domain isn't visible there yet.

January 2025 - Email Geeks
Marketer view

Email marketer from Quora suggests implementing DMARC (Domain-based Message Authentication, Reporting & Conformance) in addition to SPF and DKIM to provide instructions to receiving mail servers on how to handle emails that fail SPF and DKIM checks, enhancing overall email security.

August 2023 - Quora
Marketer view

Email marketer from Litmus stresses the importance of consistent monitoring of your email authentication setup and deliverability metrics to quickly identify and address any issues that may arise due to changes in your sending infrastructure or email practices.

April 2022 - Litmus
Marketer view

Email marketer from Mailjet shares that setting up an SPF record involves creating a TXT record in your domain's DNS settings that specifies which mail servers are authorized to send emails on behalf of your domain.

April 2023 - Mailjet
Marketer view

Email marketer from EmailGeeks Forum discusses the concept of 'SPF flattening,' which involves resolving all 'include:' statements in your SPF record to a list of IP addresses to avoid exceeding the DNS lookup limit and improve authentication speed.

October 2022 - EmailGeeks Forum
Marketer view

Email marketer from Reddit advises that having multiple SPF records can cause authentication failures. The recommendation is to consolidate all authorized sending sources into a single SPF record.

November 2023 - Reddit

What the experts say
4Expert opinions

Experts emphasize the importance of precise SPF record configuration to prevent deliverability issues. Key aspects include avoiding overly broad IP ranges (like entire colo spaces), ensuring accurate bounce handling based on the 5321.from address, maintaining up-to-date SPF records reflecting infrastructure changes, and adhering to DNS lookup limits. Implementing DMARC to handle authentication failures is also crucial for maximizing deliverability benefits.

Key opinions

  • IP Range Specificity: Avoid listing entire colo spaces in SPF; use directly assigned IPs to prevent potential forging and poor deliverability.
  • Bounce Handling Alignment: Align SPF records with bounce handling practices, particularly concerning the 5321.from address and NGP inclusion.
  • SPF Record Maintenance: Keep SPF records updated to reflect infrastructure changes and sending sources to avoid authentication failures.
  • DMARC Implementation: Implement DMARC (starting with 'p=none') to manage emails failing authentication, optimizing benefits for mailbox providers.
  • Common SPF Mistakes: Multiple SPF records and exceeding DNS lookup limits can cause issues.

Key considerations

  • Potential Forging Risks: Broad IP ranges in SPF increase the risk of domain forging and can negatively impact Gmail deliverability.
  • Sender Authentication Strategy: Design your authentication strategy with clear directives for handling authentication failures.
  • Ongoing SPF Management: Regularly review and update SPF records as your email infrastructure evolves.
Expert view

Expert from Email Geeks asks if the domain is used in the 5321.from address and whether bounces are correctly captured and sent back to NGP. Suggests that if not, an SPF record including NGP values may not be necessary for that domain.

December 2023 - Email Geeks
Expert view

Expert from Email Geeks advises against listing an entire colo space in the SPF record due to potential forging risks and recommends listing only directly assigned IPs. Mentions the potential of poor delivery at Gmail because of this type of error.

November 2024 - Email Geeks
Expert view

Expert from Word to the Wise explains that DMARC provides benefits to all mailbox providers, but those benefits are only realized if the sending side properly implements DMARC. Implementing DMARC ensures that receivers understand how a sender treats messages that fail authentication. You want to start with 'p=none' to observe.

October 2023 - Word to the Wise
Expert view

Expert from SpamResource explains that common SPF mistakes include having multiple SPF records, failing to update the SPF record when sending infrastructure changes, and exceeding the DNS lookup limit. Also, make sure all sending sources are defined within the SPF record, to avoid failures.

November 2022 - SpamResource

What the documentation says
6Technical articles

The documentation highlights the importance of SPF and DKIM as key email authentication methods. SPF verifies that emails are sent from authorized IP addresses for a given domain, preventing sender address forging. DKIM uses cryptographic authentication to verify the sender's domain and message integrity. Maintaining only one SPF record is crucial. Google Postmaster Tools provides essential insights into email sending reputation and deliverability, while RFC documents offer technical specifications for both SPF and DKIM implementations.

Key findings

  • SPF Purpose: SPF authenticates email by verifying if the sending IP is authorized by the domain's administrators.
  • DKIM Purpose: DKIM verifies the sender's DNS domain and ensures message integrity through cryptographic authentication.
  • Single SPF Record: Maintaining only one SPF record for a domain is essential.
  • Postmaster Tools: Google Postmaster Tools helps monitor email sending reputation and identify deliverability issues.
  • RFC Specifications: RFC 4408 and RFC 6376 provide technical details for SPF and DKIM standards, respectively.

Key considerations

  • Implementation Complexity: Proper implementation requires understanding technical specifications of SPF and DKIM.
  • Authentication Benefits: Using SPF and DKIM improves email deliverability and prevents sender address forging.
  • Monitoring Importance: Regularly monitor sending reputation through Google Postmaster Tools to ensure continued deliverability.
Technical article

Documentation from Google Workspace Admin Help explains that Sender Policy Framework (SPF) is an email authentication method designed to detect forging sender addresses during the delivery of email. SPF allows receiving mail servers to check that a message claiming to come from a specific domain is submitted by an IP address authorized by that domain's administrators.

August 2023 - Google Workspace Admin Help
Technical article

Documentation from RFC 6376 specifies the DomainKeys Identified Mail (DKIM) Signatures standard, outlining the technical details of how DKIM signatures are generated, verified, and used to authenticate email messages.

June 2021 - RFC 6376
Technical article

Documentation from Microsoft Learn explains how to set up SPF records to authenticate outbound email from your Microsoft 365 domain. The documentation emphasizes the importance of having only one SPF record for your domain.

January 2023 - Microsoft Learn
Technical article

Documentation from RFC 4408 provides the technical specification for the Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, detailing the syntax, semantics, and implementation considerations for SPF records.

March 2023 - RFC 4408
Technical article

Documentation from Postmark explains that Google Postmaster Tools provides valuable insights into your email sending reputation, spam rate, and other deliverability metrics, helping you identify and address any issues affecting your email performance with Gmail users.

July 2021 - Postmark
Technical article

Documentation from DKIM.org explains that DomainKeys Identified Mail (DKIM) is an email authentication system designed to verify the DNS domain of an email sender and the integrity of the message. It uses cryptographic authentication.

August 2023 - DKIM.org