6 ways to avoid SPF failures if you are reaching the DNS lookup limit

6 ways to avoid SPF failures if you are reaching the DNS lookup limit

Oct 21, 2021, 8:59:54 AM Business

If you send a lot of emails on a regular basis, you are probably aware of email authentication methods like DKIM, SPF, and DMARC. Several problems may occur when implementing these protocols for your domain. If not addressed quickly, these will be rendered ineffective and will provide no protection.

In this blog, we’ll be discussing one of the most prevalent errors faced by users with SPF implemented on their domains: Too many DNS lookups.


But for those unfamiliar with what SPF is, here’s a refresher.


SPF (Sender Policy Framework)

Sender Policy Framework, like DKIM, is an email authentication protocol that enables domain owners to designate which email servers are allowed to send emails from their domain or domains.


SPF detects fraudulent sender addresses when the email is being sent. It is restricted, however, to identifying a forged sender claim in the email’s envelope, which is used when the email bounces. When used in conjunction with DMARC, SPF detects email spoofing, a typical phishing scheme in which the email address or domain name of a reputable firm or trusted acquaintance is used.

 

Ways to Avoid SPF failures

The SPF specification restricts the number of DNS lookups to a maximum of ten. This restriction helps mailbox providers use fewer resources while verifying SPF data. If you surpass this limit, the SPF check will fail. A DNS lookup necessitates the mailbox provider to request information for a domain from the DNS, resulting in longer processing times and the usage of additional computer resources.

So what measures can be taken to avoid reaching the DNS limit? We’ve got SIX for you!


  • Use lesser INCLUDE statements

An include statement is a method in your SPF record that sends DNS lookups to another domain’s SPF record in order to validate any of their permitted IPs. Each include statement in the originating SPF record and any SPF records pointed to counts toward the maximum of ten.



You must also verify that each include statement in your SPF record is relevant and absolutely cannot be substituted by another method such as the ip4 and ip6 mechanisms.


  • Implement ip4 and ip6 mechanisms

When you have the opportunity, replace your include statement with the ip4 or ip6 mechanism to minimize the number of DNS lookups. To specify a static IP range in your SPF record, utilize the ip4 and ip6 methods. This negates the requirement for an include statement, which refers to the SPF record of another domain, thus helping you avoid going over the lookup limit.


  • Avoid resolving to the same domain

Remove any mechanisms from your SPF record that resolve to the same domain to minimize needless DNS lookups.


  • Avoid ptr Mechanisms

The SPF standard advises against using the ptr method in your SPF record. The ptr mechanism is a DNS record that maps an IP address to a domain or hostname. You should avoid utilizing this method since it might result in a high number of DNS lookups, leading to the limit of 10 being exceeded.


  • Remove Unnecessary Vendor Domains

Include statements are used by senders to direct the SPF check to a vendor or partner’s SPF record as their IP addresses frequently change. Using a partner’s or vendor’s include statement relieves the sender of the need to constantly update those changing IP ranges in their own SPF record.


  • Reference to Domains That are Currently Active

You should ensure that the domains you mention truly resolve to an active SPF record. If they don’t, they should be deleted.

These six pointers will help you avoid any unnecessary errors that might pop up while implementing SPF for your domain. Another thing to keep in mind is to avoid using incorrect syntax while deploying SPF. If you want to verify and check your newly created SPF record, use our free SPF record checker tool now!

Published by Pintu Bhatt

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