In this article, we will explore how to optimize SPF record easily for your domain. For enterprises as well as small businesses who are in possession of an email domain for sending and receiving messages among their clients, partners and employees, it is highly probable that an SPF record exists by default, which has been set up by your inbox service provider. No matter if you have a pre-existent SPF record or you need to create a new one, you need to optimize your SPF record correctly for your domain in order to ensure that it causes no email delivery issues.

Some email recipients strictly require SPF, which indicates that if you do not have an SPF record published for your domain your emails may be marked as spam in your receiver’s inbox. Moreover, SPF helps in detecting unauthorized sources sending emails on behalf of your domain.

Let us first understand what is SPF and why do you need it?

Key Takeaways

SPF is a crucial email authentication protocol that helps prevent email spoofing by specifying authorized IP addresses for sending emails.
Publishing a correctly formatted SPF record in your domain’s DNS is essential for ensuring proper email delivery and preventing spam classification.
Exceeding the 10 DNS lookup limit when configuring SPF can lead to errors and result in email delivery issues.
Regularly checking and optimizing your SPF record can help avoid common challenges, such as syntax errors and multiple SPF records for the same domain.
Using automated tools can simplify the process of managing and optimizing your SPF record to meet email security standards efficiently.

Sender Policy Framework (SPF)

SPF is essentially a standard email authentication protocol that specifies the IP addresses that are authorized to send emails from your domain. It operates by comparing sender addresses against the list of authorized sending hosts and IP addresses for a specific domain that is published in the DNS for that domain.

SPF, along with DMARC (Domain-based Message Authentication, Reporting and Conformance) is designed to detect forged sender addresses during email delivery and prevent spoofing attacks, phishing, and email scams.

It is important to know that although the default SPF integrated into your domain by your hosting provider ensures that emails sent from your domain are authenticated against SPF if you have multiple third-party vendors to send emails from your domain, this pre-existent SPF record needs to be tailored and modified to suit your requirements. How can you do that? Let’s explore two of the most common ways:

Creating a brand new SPF record
Optimizing an existing SPF record

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Instructions on How to Optimize SPF Record

Create a Brand New SPF Record

Creating an SPF record is simply publishing a TXT record in your domain’s DNS to configure SPF for your domain. This is a mandatory step that comes before you start on how to optimize SPF record. If you are just starting out with authentication and unsure about the syntax, you can use our free online SPF record generator to create an SPF record for your domain.

An SPF record entry with a correct syntax will look something like this:

v=spf1 ip4:38.146.237 include:example.com -all

v=spf1	Specifies the version of SPF being used
ip4/ip6	This mechanism specifies the valid IP addresses that are authorized to send emails from your domain.
include	This mechanism tells the receiving servers to include the values for the SPF record of the specified domain.
-all	This mechanism specifies that emails that are not SPF compliant would be rejected. This is the recommended tag you can use while publishing your SPF record. However it can be replaced with ~ for SPF Soft Fail (non-compliant emails would be marked as soft fail but would still be accepted) Or + which specifies that any and every server would be allowed to send emails on behalf of your domain, which is strongly discouraged.

If you already have SPF configured for your domain, you can also use our free SPF record checker to lookup and validate your SPF record and detect issues.

Common Challenges and Errors while Configuring SPF

1) 10 DNS Lookup limit

The most common challenge faced by domain owners while configuring and adopting SPF authentication protocol for their domain, is that SPF comes with a limit on the number of DNS lookups, which cannot exceed 10. For domains relying on multiple third-party vendors, the 10 DNS lookup limit exceeds easily which in turn breaks SPF and returns an SPF PermError. The receiving server in such cases automatically invalidates your SPF record and blocks it.

Mechanisms that initiate DNS lookups: MX, A, INCLUDE, REDIRECT modifier

2) SPF Void Lookup

Void lookups refer to DNS lookups which either return NOERROR response or NXDOMAIN response (void answer). While implementing SPF it is recommended to ensure DNS lookups do not return a void answer in the first place.

3) SPF Recursive loop

This error indicates that the SPF record for your specified domain contains recursive issues with one or more of the INCLUDE mechanisms. This takes place when one of the domains specified in the INCLUDE tag contains a domain whose SPF record contains the INCLUDE tag of the original domain. This leads to a never-ending loop causing email servers to continuously perform DNS lookups for the SPF records. This ultimately leads to exceeding the 10 DNS lookup limit, resulting in emails failing SPF.

4) Syntax Errors

An SPF record may exist in your domain’s DNS, but it is of no use if it contains syntax errors. If your SPF TXT record contains unnecessary white spaces while typing the domain name or mechanism name, the string preceding the extra space would be completely ignored by the receiving server while performing a lookup, thereby invalidating the SPF record.

5) Multiple SPF records for the same domain

A single domain can have only one SPF TXT entry in the DNS. If your domain contains more than one SPF record, the receiving server invalidates all of them, causing emails to fail SPF.

6) Length of the SPF record

The maximum length of a SPF record in the DNS is limited to 255 characters. However, this limit can be exceeded and a TXT record for SPF can contain multiple strings concatenated together, but not beyond a limit of 512 characters, to fit the DNS query response (according to RFC 4408). Though this was later revised, recipients relying on older DNS versions would not be able to validate emails sent from domains containing a lengthy SPF record.

Optimizing your SPF Record

In order to promptly modify your SPF record you can use the following SPF best practices:

Try typing down your email sources in decreasing order of importance from left to right in your SPF record
Remove obsolete email sources from your DNS
Use IP4/IP6 mechanisms instead of A and MX
Keep your number of INCLUDE mechanisms as low as possible and avoid nested includes
Do not publish more than one SPF record for the same domain in your DNS
Make sure your SPF record doesn’t contain any redundant white spaces or syntax errors

Note on SPF Flattening:

SPF flattening, which converts mechanisms like INCLUDE into a single list of IP addresses, can significantly reduce the number of DNS lookups in your SPF record, helping to avoid the 10 DNS lookup limit. However, it is not always recommended because:

Dynamic Infrastructure: If your email service provider updates their sending IPs, you’ll need to manually update your flattened SPF record each time, leading to high maintenance.
Record Length: Flattening can result in excessively long SPF records, which may exceed DNS query limits, causing errors.

Solution: If you choose to flatten your SPF record, you can use automated SPF flattening tools to simplify the process and keep your records updated dynamically.

Optimizing Your SPF Record Made Easy with PowerSPF

You can go ahead and try implementing all those above-mentioned modifications to optimize your SPF record manually, or you can forget the hassle and rely on our dynamic PowerSPF to do all that for you automatically! PowerSPF helps you optimize your SPF record with a single click, wherein you can:

Add or remove sending sources with ease
Update records easily without having to manually make changes to your DNS
Get an optimized auto SPF record with the single click of a button
Stay under the 10 DNS lookup limit at all time
Successfully mitigate PermError
Forget about SPF record syntax errors and configuration issues
We take away the burden of resolving SPF limitations on your behalf

Sign up with PowerDMARC today to bid adieu to SPF limitations forever!

About
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Maitham Al Lawati

Cybersecurity Expert, CEO at PowerDMARC

Maitham is a tech entrepreneur, cybersecurity expert, CEO and Founder of PowerDMARC with 15+ years of industry experience. Maitham holds a Global MBA from the University of Manchester and various professional certifications including CISSP, CISM, CRISC, and ISC2 CCSP.

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How to Optimize SPF Record?