Summary
Setting up SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) records is fundamental for email deliverability, especially in email marketing. Proper configuration ensures your emails are authenticated, reducing the likelihood of them being flagged as spam or blocked. Common pitfalls include having multiple SPF records or overly broad IP ranges, which can undermine your sender reputation. Verifying your setup with tools like Google Postmaster Tools is also critical for monitoring performance and maintaining good inbox placement.
Key findings
- Single SPF record: A domain should only have one SPF TXT record starting with v=spf1. Multiple records can invalidate your SPF authentication.
- IP range precision: Including overly broad IP ranges, such as a /18 CIDR, can allow unauthorized parties to send emails purporting to be from your domain, negatively impacting your email deliverability and potentially leading to blocklisting.
- Verification records: DNS records used for third-party service verification, like Google Postmaster Tools, should be separate TXT records and not merged into the SPF record.
- Bounce capturing: Properly capturing and processing email bounces is essential for maintaining a healthy sender reputation and avoiding blacklists. This often depends on the domain used in the Return-Path (RFC 5321.from) address.
Key considerations
- Consolidate SPF: Merge all authorized sending sources (IP addresses, include mechanisms) into a single SPF record for your domain. Learn more about where SPF, DKIM, and DMARC records should be placed.
- Specific IP authorization: Instead of wide IP ranges, list only the specific IP addresses assigned to your sending infrastructure to enhance security and improve deliverability.
- Verify SPF and DKIM: After making changes, use an SPF validation tool to ensure your record is syntactically correct and covers all your sending sources. This helps to verify your DMARC, DKIM, and SPF setup.
- Google Postmaster Tools setup: Ensure the google-site-verification string is in its own TXT record, not within your SPF record, to properly verify your domain in Google Postmaster Tools. This is crucial for understanding Google Postmaster Tools.
What email marketers say
Email marketers frequently encounter challenges when configuring SPF and DKIM records, particularly when managing emails from various platforms or handling existing DNS settings. Their concerns often revolve around practical application and troubleshooting, such as consolidating records, understanding IP ranges, and ensuring proper bounce management to maintain effective email campaigns.
Key opinions
- Confusion with multiple SPF: Many marketers are unsure why their domain has multiple SPF records and how to correct this common misconfiguration.
- IP range justification: There's often a lack of clarity regarding the necessity and implications of including large IP ranges in SPF records.
- Practical guidance: Marketers seek straightforward instructions on how to format and correct their SPF and DKIM records effectively.
- Bounce handling importance: The role of bounce capturing for specific email service providers (ESPs) like NGP is a frequent point of discussion.
Key considerations
- Merging records: It is critical to combine all legitimate sending sources into a single SPF record, rather than having multiple entries. You can see how this affects your emails if they fail to reach the inbox.
- Review IP ranges: Scrutinize any broad IP ranges included in your SPF to ensure they are genuinely necessary and not exposing your domain to spoofing.
- Validate setup: Regularly use online SPF validation tools to check for errors and ensure your records are correctly published. For example, to set up email authentication for multiple ESPs.
- Bounce capture alignment: Confirm that the domain specified in the Return-Path address is correctly set up to capture bounces, ensuring your ESP receives crucial feedback.
Marketer view
An Email Geeks marketer shares a common SPF configuration mistake, noting that they had been trying to fix multiple SPF records for a political campaign's email marketing. They were trying to get clear instructions on how to correctly format the record after using an online validator.
Marketer view
An Email Geeks marketer confirms the issue, stating that they had figured out the problem was having two separate TXT entries both starting with v=spf1. They appreciate the confirmation and alternative setup suggestions provided by the community.
What the experts say
Email deliverability experts strongly advocate for precise SPF and DKIM configurations, warning against common missteps that can severely impact sender reputation and inbox placement. They stress the importance of understanding the technical implications of broad IP ranges and the necessity of proper bounce handling, alongside accurate verification for tools like Google Postmaster Tools.
Key opinions
- No multiple SPF: Experts agree that having two separate TXT entries starting with v=spf1 is incorrect; they must be merged into a single record.
- Risks of broad IP ranges: Using wide IP ranges like a /18 for email is highly questionable and can allow others to forge your domain, leading to poor delivery, especially with providers like Gmail.
- Direct IP listing: Only IPs directly assigned to your sending infrastructure should be listed in the SPF record.
- Bounce handling is critical: Ensuring correct bounce capturing and processing, particularly if a domain is used in the 5321.from address, is vital for maintaining sender reputation.
- Google Postmaster Tools verification: The Google site verification string should reside in a separate TXT record to enable successful domain verification in Google Postmaster Tools.
Key considerations
- Syntactic correctness: Always ensure your merged SPF record is syntactically correct, combining all include mechanisms and ip4 directives into one line. Refer to what SPF means in email.
- Minimize IP space: Do not list entire colocation IP spaces unless absolutely necessary, as it can inadvertently permit spoofing by other users in that range. This is often a reason why emails fail at Microsoft.
- DMARC integration: While not directly SPF, implementing DMARC alongside SPF and DKIM provides a robust authentication layer and visibility into email delivery issues. Monitoring DMARC reports from Google and Yahoo can help identify SPF failures.
- Alignment check: Verify that your SPF authentication aligns with your sending domain in Google Postmaster Tools for optimal deliverability. Improper alignment is a common reason for SPF authentication issues.
Expert view
An Email Geeks expert advises against using two separate TXT entries both starting with v=spf1 for SPF records. They suggest merging them into a single syntactically correct record, such as v=spf1 ip4:66.96.128.0/18 include:_spf.google.com include:_spfprod.ngpvan.com ~all.
Expert view
An Email Geeks expert strongly questions the use of a /18 CIDR block for email sending, noting that this range encompasses approximately 16,000 IP addresses. Such a broad specification raises concerns about its necessity and potential security implications.
What the documentation says
Official documentation and technical guides provide the authoritative framework for implementing SPF and DKIM. They detail the syntax, mechanisms, and best practices necessary to ensure proper email authentication, highlighting how these records contribute to preventing spoofing and improving email deliverability across various mail systems.
Key findings
- SPF record uniqueness: The SPF standard strictly permits only one TXT record beginning with v=spf1 per domain to avoid authentication failures.
- Mechanism usage: Mechanisms like include are designed to incorporate authorized senders, while ip4 specifies exact IP addresses or CIDR ranges.
- DKIM principles: DKIM relies on cryptographic signatures using a public/private key pair to verify email integrity and sender authenticity, enhancing trust in email communications.
- Google Postmaster Tools: Domain verification for Google Postmaster Tools requires adding a specific TXT record to your DNS, separate from your SPF record, to prove ownership.
Key considerations
- Consolidate mechanisms: All SPF mechanisms and directives for a domain must be combined into a single TXT record to comply with the standard and prevent validation errors. For more details on common issues, see how to troubleshoot SPF authentication issues.
- Precise IP listing: When using ip4 or ip6 mechanisms, specify the narrowest possible IP ranges to minimize the risk of unauthorized use and enhance security. Incorrect configurations can lead to the SPF unauthorized mail is prohibited error.
- DNS record management: Ensure that DKIM records, which typically involve CNAME or TXT records, are correctly published in your DNS. These records are separate from your SPF and verification TXT records.
- Leverage Postmaster Tools: Utilize Google Postmaster Tools for comprehensive insights into your email performance, including spam rates, domain reputation, and authentication errors, ensuring your verification TXT record is correctly configured. More information on improving domain reputation with Google Postmaster Tools can be found here.
Technical article
Documentation from Email on Acid states that a domain can only have one SPF record. However, it's possible to have more than 10 approved IPs, and the 'include' parameter in the SPF record allows for this expansion.
Technical article
Customer.io documentation explains that to authenticate a domain, four DNS records need to be added to the DNS hosting provider for each domain used for sending. This comprehensive setup ensures robust email authentication.
Related resources
5 resources
Related pages
How to verify DMARC, DKIM, and SPF setup?
Where should SPF, DKIM, and DMARC records be placed for email authentication?
How do I align SPF authentication with my sending domain in Google Postmaster Tools?
What is the full form of SPF in email?
A simple guide to DMARC, SPF, and DKIM
Ultimate Guide to Google Postmaster Tools V2
Why Your Emails Fail: Expert Guide to Improve Email Deliverability [2025]
Why your emails fail at Microsoft: the hidden SPF DNS timeout
How to set up email authentication for multiple ESPs on the same sending domain?
How to fix the 'SPF unauthorized mail is prohibited' error
