SPF or Sender Policy Framework is an email authentication protocol that is critical in the process of preventing spoofing attacks. SPF works by specifying senders (mail servers) that are authorized to send emails on behalf of an organization’s domain.

However, SPF comes with a unique limitation: it has a DNS lookup limit of 10 queries as mentioned under section 4.6.4 of RFC 7208. SPF records that exceed this lookup limit, SPF breaks and returns a permanent error. This is where SPF flattening comes into play as an effective solution to resolve this limitation.

What is SPF Flattening?

SPF flattening simplifies and optimizes your SPF DNS record. This reduces the number of DNS lookups it generates, ensuring domain owners stay within the allowed DNS query limit. It does so by consolidating nested includes and replacing indirect references with corresponding IPs, transforming the record into a single, comprehensive entity for error-free SPF authentication.

Example:

Before Flattening: v=spf1 include:example1.com include:example2.com ~all

After Flattening: v=spf1 ip4:192.168.1.1 ip4:192.168.2.2 ~all

Flattening SPF records replaces the “include” mechanisms with direct IP addresses, minimizing DNS lookups.

Why is SPF Flattening Essential?

Simplifying SPF records by using optimization techniques like Flattening offers several benefits:

1. Maintaining Compliance

It is mandatory for SPF records to adhere to DNS lookup limits. Flattening helps simplify SPF records to stay under the limit, thereby maintaining compliance with RFC-specified regulations for email authentication protocols documented by the IETF. This compliance also ensures that your domain remains trustworthy in the eyes of email-receiving mail servers.

2. Improved Email Deliverability

Emails that exceed the SPF lookup limit are often treated with suspicion and may get flagged or even rejected by the receiver’s mail server. This will lead to email deliverability issues. SPF flattening ensures that your SPF stays within the permitted limit, thereby making your emails appear more legitimate and resolving deliverability issues.

3. Reduced Risk of Email Spoofing

Pairing SPF with DMARC, while also using flattening to optimize SPF, reduces the risk of email-based cyber attacks like phishing and spoofing. If your DMARC implementation is paired with SPF that exceeds the allowed limit, failing SPF will also result in DMARC failures for even legitimate messages.

How SPF Flattening Works

You can flatten SPF manually, or choose an automated online tool to fast-track the method. Let’s explore both:

Manual SPF Flattening

To manually flatten your SPF records:

Step 1. Analyze SPF Records: Identify all includes and nested lookups.

Step 2. Consolidate Lookups: Replace includes with direct IP addresses or CIDR ranges.

Step 3. Test the Flattened Record: Validate your flattened SPF record by either manually reviewing the record in your DNS, or using an online SPF checker tool to ensure compliance and functionality.

Automated SPF Flattening

You can auto-flatten your SPF records using PowerDMARC’s SPF flattening tool. Here’s how it works:

Step 1: Sign up on the PowerDMARC platform.

Step 2: Click on PowerSPF under “Hosted Services”.

Step 3: Add your domain and select the active domain.

Step 4: Click on “Automated Setup” and Enable PowerSPF.

Note: Manual SPF flattening is not recommended as email service providers often add or change their IP addresses without notifying users. Users need to always stay on top of these services to stay informed on any changes. Unless they do so, it may lead to unwanted SPF failures and cause your legitimate emails to not get delivered. This makes automatic flattening a hassle-free method and a clear winner in terms of both reliability and effectiveness.

Best Practices for Implementing SPF Flattening

To ensure the flattened SPF record is performing as it should, you can take the following tips into consideration:

1. Monitor Flattened SPF Records

SPF records are often subject to changes as they heavily depend on alterations made by your email service providers and vendors to their own IP addresses and sending servers. Flattened SPF records (especially ones that are manually flattened) may often get outdated – reintroducing lookup limitation errors. It’s important to schedule periodic reviews to check for any changes and update your SPF records accordingly.

2. Simplify SPF Records

While flattening SPF records, you need to also keep in mind simplicity and manageability. Extensive and complicated SPF setups often introduce errors and complexities during authentication. As flattening replaces include mechanisms with IP addresses and ranges, sometimes the string may get long enough to exceed the permitted SPF length limit of 255 characters.

3. Use SPF Macros

A much more effective and reliable method that does away with the drawbacks of SPF flattening is Macros optimization. This method ensures lookup, void as well as length limits are not exceeded in almost all cases, with a much lesser failure rate in comparison to flattening.

Challenges of SPF Flattening and How to Overcome Them

Let’s explore a few problems domain owners may face when using traditional flattening methods, and some easy fixes:

1. Managing Updates

Changes in authorized servers require updates to flattened records. A solution around this is to schedule regular audits and use automated tools.

2. Lengthy SPF Records

Replacing IP references with actual IPs may lead to very lengthy records that exceed the character length limit. A solution around this is to use Macros instead of flattening.

3. Misconfigured SPF Records

Misconfigured records can cause email disruptions. Rely on trusted SPF flattening tools or services that also offer expert support for assistance whenever needed.

Feature	SPF Flattening	SPF Macros
Definition	Converts all include mechanisms into direct IP addresses.	Uses the %{i}, %{s}, and %{h} macros to resolve SPF lookups dynamically.
Purpose	Reduces the number of DNS lookups by replacing includes with IPs.	Dynamically adjusts SPF lookups to avoid exceeding the 10 DNS lookup limit.
Pros	- Reduces additional DNS lookups. - Improves SPF record efficiency.	- Keeps SPF records shorter. - Avoids excessive DNS lookups dynamically.
Cons	- Requires manual updates when IPs change. - Can make SPF records too long.	- Can be complex to implement correctly without assistance
Best suited for	Organizations with stable IP addresses and a need to reduce SPF lookups.	Advanced users needing dynamic SPF solutions without static IP lists.

Why SPF Flattening Matters for Your Email Strategy

SPF flattening is an essential practice for organizations relying on email for communication. By addressing SPF lookup limits, you can ensure uninterrupted email delivery, strengthen your defenses against spoofing, and optimize your email strategy.

Take Action Today: Begin implementing SPF flattening to secure your domain and improve email deliverability. Need help? Contact us to explore automated SPF flattening tools to simplify the process.

FAQs

Does SPF Flattening Have Limitations?

SPF Flattening does come with a set of limitations making macros a more effective alternative. Let’s explore what these are below:

Flattening Requires Manual Updates: SPF flattening requires constant manual updates whenever your email vendors change or add to their IPs.
Flattening Can Lead to Length Limitations: Flattened SPF records can get very long and easily exceed the SPF record length limit, leading to errors.
Potential SPF Failures: As traditional flattening doesn’t lead to dynamic IP updates, it can lead to SPF failures.
Complexity in Management: Since SPF flattening needs regular manual interventions and updates, it can introduce a lot of complexity for organizations using multiple third-party email vendors.

How Does SPF Flattening Adapt to New Email Senders?

Dynamic SPF flattening services or automated flattening tools like PowerSPF can adapt to new email senders. However, the same cannot be said for traditional methods of flattening. In traditional flattening, email senders do not get auto-updated in the sender’s SPF record which may lead to unwanted authentication failures.

How SPF Flattening Ensures Compliance with Verified Email Senders

SPF flattening helps maintain compliance by including only authorized IPs and verified email senders. This reduces the risk of unauthorized email relay. Flattening services optimize SPF records to avoid exceeding the 10 DNS lookup limit, ensuring compliance with RFC limitations. This is especially true for organizations using automated or manual checks, ensuring their SPF records are always up-to-date.

How does SPF Flattening handle duplicate senders and overlapping IP ranges?

To efficiently manage duplicate and overlapping IPs, SPF flattening removes redundant entries and consolidates duplicate IPs, thereby simplifying a domain’s SPF records. It can merge overlapping IP ranges and ensure that all listed IPs belong to verified senders with no conflicting entries.

About
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Yunes Tarada

Domain & Email Security Expert at PowerDMARC

Yunes is an Operations Team Lead at PowerDMARC with expert knowledge in email authentication and security. Yunes is a Microsoft-certified Azure Administrator Associate with certifications in CompTIA A+ and many more.

SPF flattening: What is it and why do you need it?