Understanding SPF Lookup And Ways To Avoid SPF Lookup Failures

SPF lookups are used for analyzing the SPF records of a domain to check for security risks, errors, and authorized IP addresses. It allows a user to specify an IP address for checking its authorization for sending emails on behalf of the domain. The SPF lookup will analyze the registered TXT records in run-time and help get detailed diagnostics of the SPF record.

spf too many dns lookups

Mechanisms for SPF lookups

An SPF lookup directs the mailbox provider to request information about a domain from the DNS. Thus, The modifiers and mechanisms used for SPF lookups are:

  • include
  • a
  • MX
  • ptr (do not use)
  • exists
  • redirect

Since it leads to greater use of computer resources and slower processing times, there is an SPF lookup limit of 10. It is a limit defined in the SPF specification to reduce the number of system resources a mailbox provider will use when checking multiple SPF records. Users who exceed this limit get a permerror SPF – permanent error too many DNS lookups.

​Steps To Avoid SPF Lookup Failure

There are many ways users can avoid the SPF too many DNS lookups and other SPF lookup failures:

SPF flattening

It is one of the best SPF lookup counters to avoid reaching the SPF lookup limit. It means putting the IP addresses in place of all the domains in the SPF record. There are two ways of performing SPF flattening – manual and automatic. There is an inherent problem with manual SPF flattening because the mailbox providers may add or change the IP addresses without alerting the user, which leads to the same email delivery problems.

Avoid unnecessary include statements

There is a mechanism in the SPF record that will redirect the SPF lookup to another domain’s SPF record to verify the authorized IPs. This mechanism is the include statement, and each include statement in the SPF record is counted to the limit of 10. For ensuring the SPF lookup doesn’t return a failure, it is crucial to ensure that every include statement in the SPF record is essential and cannot get replaced by other mechanisms like the ip4 and ip6.

SPF Compression

It is an essential tool that compliments every DMARC project. It offers a fast, smart, and safe way to reach the DMARC reject policy, reduce the risk, and save time when performing SPF lookups. You can rest assured that the SPF lookup limit will never get exceeded with SPF compression for your business domain.

Use ip4 and ip6 mechanisms

These mechanisms are used for listing static IP ranges in the SPF record, which eliminates the requirement of an include statement for referencing another domain’s SPF record. Hence ip4 or ip6 mechanisms can be used to avoid SPF lookup failure.

Avoid ptr mechanisms

A crucial recommendation for avoiding SPF lookup failure is not using the ptr mechanism in the SPF record, which is a type of DNS record that links the IP address to a host or domain name. The inherent issue with using the ptr mechanism is that it results in many DNS lookups, which quickly exceeds the SPF lookup limit.

Remove legacy vendor and partner domains

The domain owners must remove the include statements, redirecting the SPF lookup to legacy partners or vendor’s SPF record, which no longer sends emails on their behalf. It will help avoid unnecessary DNS lookups.

Reference actively sending domains only

Another method to avoid SPF lookup failure is to ensure that the reference domains must include active SPF records or else, they must be removed.

Domain owners use SPF records for publishing a list of IP addresses that they have authorized for sending emails on their behalf. Thus, they can make it harder for malicious actors to gain unauthorized access or inject spam by disguising their identity. SPF lookup is a crucial diagnostic tool that displays essential information about the registered SPF records, which domain owners must employ when they come face-to-face with any SPF errors.

multiple spf records

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