How To Use An SPF Record Tester To
Prevent Email Spoofing


Sender Policy Framework (SPF) is an email authentication protocol that helps prevent email spoofing by allowing domain owners to specify which mail servers are authorized to send emails on their behalf. SPF records are added to the Domain Name System (DNS) as a TXT record, specifying which IP addresses and servers are permitted to send emails for the domain.

Email spoofing is a common technique used in phishing attacks, where malicious actors forge sender addresses to make their emails appear as though they originate from a trusted source. Without a properly configured SPF record, malicious senders can easily impersonate your domain, leading to potential data breaches, loss of credibility, and email deliverability issues.


Steps to Use an SPF Record Tester


Identifying Your Current SPF Record

Prior to verifying your SPF record, it's essential to check if your domain has an existing one. This can be accomplished through various online SPF lookup services or by utilizing command-line tools such as nslookup. For a manual check of your SPF record, you can execute the command below:

nslookup -type=TXT yourdomain.com

If an SPF record exists, it will appear in the output, showing which mail servers are authorized to send emails on behalf of your domain.



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Choosing an SPF Record Testing Tool

Prior to verifying your SPF record, it’s essential to check if your domain already possesses an existing one. This can be accomplished through various online SPF lookup services or by utilizing command-line tools such as nslookup. To manually inspect your SPF record, you may execute the command below:

Some popular SPF record testing tools include:

  • MXToolbox SPF Record Checker

  • SPF Record Tester by Kitterman

  • Google Admin Toolbox SPF Check

  • DNSstuff SPF Lookup Tool

Running an SPF Record Test

After choosing an SPF record testing tool, input your domain name into the designated field and initiate the test. The tool will fetch the SPF record linked to your domain and deliver an in-depth evaluation of its correctness, highlight any configuration errors, and offer suggestions for enhancement.


Interpreting the SPF Record Test Results

After running the test, you will receive a report that typically includes:

  • SPF Record Validity: Indicates whether your SPF record is correctly formatted and properly structured.

  • IP Address Authorization: Lists the IP addresses and mail servers allowed to send emails on behalf of your domain.

  • Multiple SPF Records: Highlights if there are multiple SPF records, which can cause authentication failures.

  • SPF Record Length: Ensures your SPF record does not exceed the 255-character limit imposed by DNS specifications.

  • Syntax and Configuration Errors: Identifies any mistakes, such as missing or incorrect mechanisms.

Troubleshooting and Fixing SPF Record Issues


Handling Multiple SPF Records

A frequent problem encountered with SPF setup is the presence of several SPF records within your DNS. This situation can result in failures during SPF authentication. As a domain can contain only one SPF record, it’s essential to merge any existing records into a single one, ensuring that you use the appropriate syntax.

For example, if you have:

v=spf1 ip4:192.168.1.1 -all

v=spf1 include:_spf.example.com ~all

You should merge them into:

v=spf1 ip4:192.168.1.1 include:_spf.example.com -all


Ensuring SPF Record Length Compliance

SPF records need to adhere to the 255-character maximum for DNS queries. Should your SPF record surpass this limit, consider streamlining it by eliminating redundant mechanisms or delegating using subdomains.

Should the record grow excessively long, you have the option to utilize the include feature to point to extra SPF records managed by external providers, rather than enumerating every IP address directly. Click the link to find out more.



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Resolving Syntax Errors

Incorrect syntax in SPF records can cause authentication failures. Common syntax mistakes include:

  • Missing spaces between mechanisms

  • Incorrect use of qualifiers (+, -, ~, ?)

  • Improper formatting of IP addresses

Always validate your SPF record syntax using SPF testing tools before deploying changes to avoid potential email delivery issues.


Enhancing Email Security with SPF, DKIM, and DMARC


Although SPF is effective in combating email spoofing, it should not be relied upon alone. To enhance your email security, it’s essential to also adopt DomainKeys Identified Mail (DKIM) and Domain-based Message Authentication, Reporting, and Conformance (DMARC).

  • DKIM: Adds a digital signature to your emails, verifying their authenticity and ensuring they have not been altered in transit.

  • DMARC: Enforces email authentication policies by combining SPF and DKIM, allowing domain owners to specify how email providers should handle messages that fail authentication checks.