DMARC (Domain-based Message Authentication, Reporting, and Conformance) is a tool that helps protect email domains from being used for spam or phishing. But how does DMARC interact with DNS (Domain Name System) caching and load? Here’s a simple explanation.

What Is DNS Caching?

When you visit a website, your computer uses the DNS to translate the website’s name into an IP address, which is like a phone number for computers. To speed up this process, your computer stores, or “caches”, some of this information so it doesn’t have to look it up every time. This is called DNS caching.

How Does DMARC Use DNS?

DMARC policies are communicated using the DNS. This means that when an email is sent, the receiving server uses the DNS to look up the DMARC policy for the domain that sent the email.

What Are the Considerations for DNS Caching and DMARC?

There’s a balance to be struck between keeping the DMARC policy information up to date (“freshness”) and reducing the load on the DNS by using cached information.

  • Short TTLs (Time to Live): If the DMARC policy has a short TTL, it means the information is updated frequently. But this can cause problems. If a lot of emails are sent in a short time, it could overwhelm the DNS with requests for the DMARC policy. This could slow down the DNS or even cause it to crash.
  • Long TTLs: If the DMARC policy has a long TTL, it means the information is updated less frequently. This reduces the load on the DNS, but it can also cause problems. If the DMARC policy is changed, it could take a long time for the new policy to be used because the old policy is still cached.

So, when setting the TTL for a DMARC policy, it’s important to find a balance. The TTL should be long enough to reduce the load on the DNS, but short enough to ensure that changes to the DMARC policy are used quickly.

Remember, this is a simplified explanation. In reality, using DMARC involves a lot of complex processes and technologies. But hopefully, this gives you a basic understanding of how DMARC interacts with DNS caching and load.

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