---
title: "Why subdomains should not inherit the SPF policy of the parent domain? | AutoSPF"
description: "It’s common for businesses to have multiple subdomains, but what about their security?"
image: "https://autospf.com/og/blog/why-subdomains-should-not-inherit-the-spf-policy-of-the-parent-domain.png"
canonical: "https://autospf.com/blog/why-subdomains-should-not-inherit-the-spf-policy-of-the-parent-domain/"
---

Quick Answer

It’s common for businesses to have multiple subdomains, but what about their security? While some domain owners completely ignore securing their subdomains, some subject them to the SPF policy of the parent domain. Yes, the latter is definitely better than the former, but even that doesn’t promise robust defense against phishing, spoofing, and ransomware attacks attempted by exploiting your domain.

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![SPF policy](https://media.mailhop.org/autospf/images/2024/08/kitterman-spf-2522.jpg) 

It’s common for businesses to have multiple subdomains, but what about their security? While some domain owners completely ignore securing their subdomains, some subject them to the SPF policy of the parent domain. Yes, the latter is definitely better than the former, but even that doesn’t promise robust defense against phishing, spoofing, and [ransomware attacks](https://www.darkreading.com/cyberattacks-data-breaches/ransomhub-actors-exploit-zerologon-vuln-in-recent-ransomware-attacks) attempted by exploiting your domain.

Moreover, there are some drawbacks if subdomains inherit the SPF policy of the parent domain. _This blog discusses what these drawbacks are, convincing you to build separate SPF records for all your domains and subdomains_.

## Primary reasons

### 1\. Different email-sending sources

Subdomains are usually dedicated to different operations of an organization or separate entities within an organization with their own [email infrastructure](https://www.voilanorbert.com/blog/email-infrastructure/). So, inheriting the [SPF record](/spf-record-checker/create-spf-record/) of the main domain can negatively impact authorized email sources that aren’t linked with the subdomain. 

Whereas if each subdomain has an independent SPF record, the domain owner has granular control. This ensures they have precise control over email-sending sources, minimizing security gaps.

### 2\. SPF record size issues

SPF records have a 255-character limit per [DNS TXT record](https://www.cloudflare.com/learning/dns/dns-records/dns-txt-record/) and a 512-byte limit for DNS responses. If a main domain has a complex SPF record, inheriting it across multiple subdomains could lead to lengthy SPF records, increasing the risk of exceeding these limits.

Such SPF records also require more [DNS lookups](https://www.techopedia.com/definition/29029/dns-lookup), exceeding the maximum of 10\. If an SPF record exceeds this limit, it becomes invalid, and no authentication checks occur. 

### 3\. Security considerations

If a subdomain inherits the main domain’s SPF record that is overly permissive, then there is a possibility that it inadvertently authorizes [mail servers](https://www.techtarget.com/whatis/definition/mail-server-mail-transfer-transport-agent-MTA-mail-router-Internet-mailer) that you should not trust for that subdomain. Moreover, in conditions where a subdomain is used by a different business unit or partner, sharing or inheriting SPF records opens more avenues for [cyber breaches](https://www.crn.com/news/security/2024/10-major-cyberattacks-and-data-breaches-in-2024-so-far). 

![cyber breaches](https://media.mailhop.org/autospf/images/2024/08/spf-record-syntax-6.jpg) 

### 4\. DMARC alignment

[DMARC](/10-reasons-for-regular-spf-record-checks-in-cybersecurity/dmarc-record-check/) works efficiently only when the SPF record aligns with the ‘From’ address of the email sent from your domain. Different subdomains may have different DMARC policies, so inheriting the main domain’s SPF record might lead to alignment issues, reducing the effectiveness of DMARC.

### 5\. Operational flexibility

Different subdomains may require different email policies, especially in large organizations with diverse email needs. Independent SPF records allow for flexibility and customization in [email authentication](/blog/ushering-a-new-era-of-security-google-and-yahoos-take-on-email-authentication/) policies, ensuring that each subdomain operates according to its specific requirements.

For example, for a subdomain dedicated to the finance department, you can’t afford an email-based breach, and that’s why you need to set your SPF record to p=reject. Whereas, for the customer support subdomain, you can’t use the strictest policy (p=reject) because you still want your messages to reach the recipients’ inboxes, even if they sit in the [spam folder](https://www.foxnews.com/tech/big-bucks-hiding-spam-folder) in case of false positives. 

![spam folder](https://media.mailhop.org/autospf/images/2024/08/kitterman-spf-2523.jpg) 

## What you should do instead

Create individual SPF records for all the [domains and subdomains](https://thehackernews.com/2024/02/8000-subdomains-of-trusted-brands.html) you own, ensuring they are configured to fulfill specific needs. _Also, while you adjust SPF, remember to align it with DMARC policy so that there are no conflicts and contradictions_. 

Optimize SPF records to avoid excessive DNS lookups and stay within the 10-lookup limit. This can involve consolidating IP ranges or removing outdated or unnecessary entries. You can also use our [automatic SPF flattening](/) tool to sort this issue. Please [reach out to us](/contact-us/) to learn more.

## Topics

[ DMARC ](/tags/dmarc/)[ SPF ](/tags/spf/)[ SPF Flattening tool ](/tags/spf-flattening-tool/)[ SPF record ](/tags/spf-record/) 

![Brad Slavin](https://media.mailhop.org/autospf/images/authors/brad-slavin.jpg) 

[ Brad Slavin ](/authors/brad-slavin/) 

General Manager

Founder and General Manager of DuoCircle. Product strategy and commercial lead for AutoSPF's 2,000+ customer base.

[LinkedIn Profile →](https://www.linkedin.com/in/bradslavin) 

## Ready to get started?

Try AutoSPF free — no credit card required.

[ Book a Demo ](/book-a-demo/) 

## Related Articles

[  Intermediate 3m  3 points to consider before setting your SPF record to -all (HardFail)  May 22, 2025 ](/blog/3-points-to-consider-before-setting-your-spf-record-hardfail/)[  Intermediate 6m  6 Best practices for maintaining an SPF record  Jun 5, 2025 ](/blog/6-best-practices-for-maintaining-an-spf-record/)[  Intermediate 3m  Adding your SPF record to your domain provider  Sep 2, 2024 ](/blog/adding-your-spf-record-to-your-domain-provider/)[  Intermediate 6m  Your SPF record is broken- What does it mean and how do you fix it?  Jan 16, 2025 ](/blog/broken-spf-record-meaning-and-how-to-fix-it/)

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