Can I have multiple SPF records for one domain?

No, a domain should only have one SPF TXT record. If multiple SPF records are found, receiving mail servers will typically ignore them, leading to SPF authentication failures. All authorized senders for your domain should be consolidated into a single SPF TXT record.

What happens if I don't have an SPF record?

Without an SPF record, your domain is highly vulnerable to email spoofing and phishing attacks. Legitimate emails from your domain are also more likely to be flagged as spam or rejected by recipient mail servers, negatively impacting your email deliverability and sender reputation.

Is SPF alone enough for email security?

While SPF is crucial, it's not sufficient on its own for complete email security. For comprehensive protection against email fraud and spoofing, SPF should be implemented alongside DKIM and DMARC . DMARC provides policies for handling unauthenticated mail and offers valuable reporting capabilities.

What is SPF flattening and why is it important?

SPF flattening is a technique used to resolve all include mechanisms and other DNS-querying mechanisms in an SPF record into their underlying IP addresses. This helps to avoid exceeding the 10-DNS-lookup limit , preventing SPF authentication failures.

How often should I review my SPF record?

You should review your SPF record whenever you make changes to your email sending infrastructure, such as adding or removing email service providers, or changing your hosting. Even without infrastructure changes, a periodic review (e.g., quarterly) is a good practice to ensure accuracy and prevent issues.

What DNS record type is used for SPF? - SPF - Email authentication - Knowledge base

An email envelope protected by a shield, illustrating email authentication through SPF DNS records.

When setting up email authentication, one of the first questions people often ask is about the specific DNS record type required for SPF. Understanding this is crucial for properly configuring your domain's email security and ensuring your messages reach the inbox.

The answer is straightforward, though it sometimes causes confusion due to a deprecated record type that was once used. Today, Sender Policy Framework (SPF) records are published as a DNS TXT record. This standard approach allows mail servers to verify that incoming mail from a domain is sent from a host authorized by that domain's administrators.

Using the TXT record type for SPF, along with DKIM and DMARC, forms the foundation of modern email authentication protocols. This setup helps to combat email spoofing, phishing, and other malicious activities, ultimately safeguarding your domain's reputation and improving your email deliverability.

Why SPF relies on TXT records

SPF's primary function is to prevent unauthorized senders from using your domain to send email. It does this by allowing domain owners to publish a list of authorized sending hosts in their DNS. When an email server receives a message, it can check the sender's domain's SPF record to determine if the sending IP address is permitted.

DNS TXT records are versatile, allowing domain administrators to store arbitrary text information in the DNS. This makes them ideal for SPF, as the SPF record itself is essentially a string of text that describes the sending policy for a domain. The record starts with v=spf1 followed by various mechanisms and modifiers that define the authorized senders and the policy for unauthorized ones.

While there was once a dedicated SPF record type (type 99), it was deprecated. The official standard now requires SPF records to be published exclusively as DNS TXT records. Attempting to use the old SPF record type can lead to validation errors and negatively impact your email deliverability. This transition was made to streamline DNS management and ensure compatibility across different systems. You can read more about this change regarding the deprecated SPF record type 99.

Example SPF TXT recordDNS

yourdomain.com IN TXT "v=spf1 include:_spf.google.com include:mail.your-provider.com -all"

Structure of an SPF TXT record

An SPF TXT record is a single string of text. It begins with v=spf1, indicating the version of SPF being used. Following this, you add various SPF mechanisms and qualifiers to define your sending policy. Common mechanisms include:

a: Authorizes the IP addresses associated with your domain's A records.
mx: Authorizes the mail exchange (MX) records of your domain.
ip4/ip6: Directly specifies IPv4 or IPv6 addresses or ranges that are authorized to send email.
include: Refers to another domain's SPF record, commonly used for third-party senders like Google Workspace or Microsoft 365.
all: A final mechanism that defines the policy for any sender not explicitly matched by previous mechanisms. It usually includes qualifiers like -all (fail), ~all (softfail), or ?all (neutral).

When creating or modifying an SPF record, it's vital to remember the 10-DNS-lookup limit. Each include, a, mx, and ptr mechanism (and exists) in your SPF record counts as a DNS lookup. Exceeding this limit will cause SPF to fail, even if your record is otherwise correctly configured. This can be a common reason why SPF might fail despite appearing correct.

Beware the 10-DNS-lookup limit

One of the most frequent causes of SPF failure is exceeding the 10-DNS-lookup limit. Each mechanism that requires a DNS query, such as include, a, mx, and ptr, counts towards this limit. If your SPF record triggers more than 10 DNS lookups, it will result in a PermError (permanent error), causing SPF authentication to fail for all your emails. Tools like SPF flattening can help mitigate this by resolving all included domains to their IP addresses at the time of publication, reducing the number of DNS lookups during validation.

Implementing and monitoring your SPF record

To implement SPF, you'll need to access your domain's DNS management interface, usually provided by your domain registrar or hosting provider. Here, you will add a new TXT record for your domain. The SPF record should be placed at the root domain (e.g., yourdomain.com) or specific subdomains if you send email from them, ensuring each subdomain has its own SPF record.

After publishing your SPF TXT record, it's essential to monitor its performance. Issues can arise from incorrect syntax, exceeding the DNS lookup limit, or changes in your sending infrastructure. Tools like DMARC monitoring platforms are invaluable for this, providing visibility into your email authentication results and helping identify potential problems. Suped, for example, offers a robust DMARC monitoring solution that simplifies the complex data from your DMARC reports.

Common SPF issues

Syntax errors: Incorrectly formatted records leading to validation failures.
DNS lookup limit: Exceeding 10 DNS lookups in one SPF record causes a permanent error.
Record not found: SPF record is missing or not properly published in DNS.
Outdated entries: Authorized IP addresses or include mechanisms become irrelevant after changes.

Solutions and best practices

Use an SPF validator: Verify your record's syntax before publishing.
Implement SPF flattening: Automatically resolve include mechanisms to IP addresses to avoid lookup limits.
Leverage DMARC monitoring: Gain visibility into SPF results. Suped offers AI-powered recommendations for fixes and a generous free plan.
Regular audits: Periodically review and update your SPF record for accurate authorization.

Suped offers a unified platform for SPF, DKIM, and DMARC monitoring, complete with real-time alerts. It's an excellent tool for ensuring your SPF record is correctly configured and continuously performs as expected, helping to secure your email ecosystem and improve your overall email deliverability rates.

Advanced SPF considerations

An abstract illustration of email security layers around a mail server.

While SPF is a critical component, it's most effective when used in conjunction with DKIM (DomainKeys Identified Mail) and DMARC (Domain-based Message Authentication, Reporting, and Conformance). DKIM adds a digital signature to your emails, verifying that the message hasn't been tampered with in transit. DMARC, on the other hand, ties SPF and DKIM together, allowing you to tell receiving mail servers how to handle emails that fail authentication, from simply reporting to quarantining or rejecting them. This layered approach provides comprehensive protection against email fraud.

Properly configured SPF TXT records are instrumental in building and maintaining a strong sender reputation. When email receivers consistently see that your domain's emails are authenticated by SPF (and DKIM/DMARC), they are more likely to trust your messages and deliver them to the inbox rather than the spam folder. Conversely, a missing or misconfigured SPF record can lead to your legitimate emails being flagged as suspicious, hurting your deliverability and potentially landing your domain on a blocklist (or blacklist).

Sender Status	SPF Check Result	Policy Action (Example with p=reject)
Legitimate sender (authorized by SPF record)	Pass	Delivered to inbox
Unauthorized sender (not listed in SPF record)	Fail	Rejected (as per DMARC policy)

The essential role of SPF for email security

The DNS record type used for SPF is, unequivocally, the TXT record. While there once was a specific SPF record type, it has been deprecated. Adhering to the current standard of using TXT records for SPF is fundamental for establishing robust email authentication, preventing spoofing, and maintaining high email deliverability.

Properly configuring and regularly monitoring your SPF TXT record, in conjunction with DKIM and DMARC, is not just a best practice, but a necessity in today's email landscape. It protects your brand, your recipients, and ensures your important communications reach their intended audience.

Suped is designed to simplify this complex process, offering comprehensive DMARC reporting and monitoring. With features like AI-powered recommendations, real-time alerts, and SPF flattening, Suped helps you achieve and maintain strong email authentication effortlessly.