Sender Policy Framework is an email authentication protocol that allows a domain owner to publish an SPF record corresponding to their name. This SPF record includes a list of IP addresses and mail servers that the domain owner officially authorizes to be used for sending emails from.
When the email reaches the recipient’s server, it extracts the SPF record corresponding to the sender’s domain to verify if the sender’s mail server or IP address is part of the SPF record. If yes, the authorization result shows a ‘pass,’ and the email lands in the primary inbox; otherwise, the authorization fails, and the message either gets marked as spam or bounces back.
The adoption of SPF is expanding, as it provides a robust defense against email spoofing and phishing attacks, ensuring the integrity of your email communications. Considering this, the USA leads with a 92% adoption rate, followed by the UK (87%), Canada (85%), and Germany (83%).
However, not all SPF records are error-free and valid, causing a problem in the authorization process. We have enlisted the SPF risk exposures in 2024.
Common SPF Risk Findings
If your SPF record highlights ‘SPF not enabled’ or ‘SPF syntax error,’ then it means there are some configurational or syntactical errors. SPF is built to have a sensitive nature so that it effectively rules out phishing and spoofing attempts. This is exactly why even a tiny error invalidates an SPF record.
Some frequent errors are-
The Use of +all Mechanism
The use of the +all mechanism is discouraged in SPF as it allows both legitimate and illegitimate emails to pass authentication checks. This way, malicious actors get to forge the sender address of an email to make it appear as if it’s coming from a trusted domain, increasing the possibilities of phishing and impersonation attacks.
Image sourced from fastercapital.com
What’s worse is that the use of the ‘+all’ mechanism negatively impacts your domain’s reputation and can even cause it to be blocked by email providers.
CIDR Notation Errors
CIDR notation is a compact way of representing IP address ranges. In the context of SPF records, it is commonly used to specify which IP addresses are allowed to send emails on your behalf.
The prefix length in CIDR notation determines the number of significant bits in the network portion of the IP address. An error occurs if the prefix length is too large or too small for the specified IP address range. An error can also erupt if there is overlap or conflict between the specified CIDR blocks, leading to ambiguity in SPF evaluation.
Mechanism Order Error
The correct order of mechanisms is important so that email receivers can interpret and enforce the SPF policy effectively. A mechanism order error occurs when the sequence of mechanisms and modifiers in the SPF record is incorrect or suboptimal, causing unintended allowlisting or blocklisting. Placing allowed mechanisms like include, a, and mx before blocked mechanisms like redirect and +all can unintentionally cause validation and authorization issues.
Also, the incorrect order of mechanisms causes problems in policy maintenance and troubleshooting. So, when SPF policies evolve or your company’s email infrastructure changes, it gets difficult to maintain a consistent and logically ordered SPF record.
The Use of the ‘ptr’ Mechanism
The use of the ‘ptr’ mechanism is highly discouraged in SPF as it requires performing a reverse DNS lookup on the IP address of the connecting client. This adds to the complexity and slows down the authentication process.
Also, while including a PTR record offers assurance regarding the domain name associated with an IP address, it doesn’t help verify the sender’s genuineness. A PTR record merely confirms the reverse mapping of an IP address to a domain name, which may not accurately reflect the sender’s identity or authorization status. Therefore, relying solely on PTR records for SPF validation may not effectively prevent email spoofing or unauthorized use of domain identities.
Exceeding the DNS Lookup Limit
A limit of 10 DNS lookups has been imposed to avoid overburdening the resources involved in the authentication process. Organizations with complex and extensive email infrastructure tend to reach this limit within no time, invalidating the SPF record and hindering the authentication process.
To fix this, we offer an automatic SPF flattening service that eliminates the need for frequent lookups. We start by performing DNS lookups for each included domain and then retrieving the corresponding IP addresses linked to each domain. This may involve querying DNS records for A (IPv4) or AAAA (IPv6) records or performing reverse DNS lookups (PTR records) for domain names.
Then, all the resolved IP addresses are consolidated into a single SPF record by removing duplicate IP addresses and aggregating IP ranges. Finally, a flattened SPF record is generated that must be published in your domain’s DNS zone.
If your SPF record has also exceeded the lookup limit, then get in touch with us for help.
