Does a subdomain used for sending emails need its own SPF record?
Michael Ko
Co-founder & CEO, Suped
Published 9 May 2025
Updated 19 Aug 2025
7 min read
The question of whether a subdomain used for sending emails needs its own Sender Policy Framework (SPF) record is a common one. It arises frequently as organizations increasingly use subdomains to manage different types of email traffic, like marketing campaigns, transactional notifications, or even internal communications.
SPF is a foundational email authentication protocol designed to prevent email spoofing. It allows domain owners to publish a list of authorized sending IP addresses in their DNS records. Receiving mail servers then check this record to verify that incoming mail from a domain is sent from an allowed server.
In short, if you are using a subdomain to send emails, yes, it absolutely needs its own SPF record. Relying solely on your root domain's SPF record for a subdomain sending emails is a common misconception that can lead to significant deliverability issues.
An SPF record is a type of DNS TXT record. It lists all the mail servers that are authorized to send email on behalf of a particular domain. When an email is sent, the recipient's mail server performs a DNS lookup to check the SPF record for the sending domain, verifying if the sending IP address is listed as legitimate.
The critical point to understand is how DNS resolves records. Each hostname, whether it's your root domain (e.g., example.com) or a subdomain (e.g., marketing.example.com), is treated as a distinct entity in the Domain Name System. When a mail server looks for an SPF record, it specifically queries for a TXT record associated with the exact domain (or subdomain) from which the email appears to originate.
This means that an SPF record published for your main domain, example.com, will not automatically apply to a subdomain like marketing.example.com. Each needs its own explicit record if it's sending mail. This is why when are separate SPF records needed for a domain and its subdomains, the answer is usually based on sending activity.
This principle ensures granular control over email sending sources. If you use a subdomain to send emails through a specific Email Service Provider (ESP), you'll add that ESP's authorization to the subdomain's SPF record. This approach helps maintain the integrity of your main domain's reputation, isolating any potential deliverability issues to the subdomain, as outlined in discussions about why subdomains should not inherit the SPF policy of the parent domain.
Consequences of a missing subdomain SPF record
Sending emails from a subdomain without a proper SPF record is akin to sending mail from your main domain without one, only perhaps with a more confusing trail. Recipient mail servers, like those run by Microsoft and Google, are increasingly strict about email authentication. If they cannot verify the sending server via SPF, the email is highly likely to be marked as spam, quarantined, or even rejected outright.
This directly impacts your email deliverability. Poor SPF configuration (or lack thereof) can lead to:
Reduced inbox placement: Emails are more likely to land in the spam folder instead of the inbox.
Damage to sender reputation: ISPs and email providers track sending behavior, and a history of unauthenticated mail can harm your overall sender reputation, affecting even other domains or subdomains you send from. This is why it's a good idea to use subdomains to improve deliverability.
Increased blocklisting (or blacklisting): Domains lacking proper authentication are more susceptible to being placed on email blocklists (or blacklists), which can severely impact all email sending from that domain.
The danger of missing SPF on subdomains
If a subdomain is used for email sending and lacks its own SPF record, receiving mail servers will not find the necessary authorization information for that specific sender. This often leads to authentication failures, even if your root domain has a perfectly valid SPF record.
This missing piece of the authentication puzzle makes your emails look suspicious, increasing the likelihood of them being flagged as spam or outright rejected. It also misses an opportunity to improve email deliverability.
Configuring SPF for subdomains
Setting up an SPF record for a subdomain is similar to setting one up for a main domain. You'll add a TXT record to your DNS settings for the specific subdomain. This record will include the IP addresses or hostnames of all authorized sending sources for that subdomain.
A common challenge arises when multiple email service providers (ESPs) send emails on behalf of the same subdomain. Each ESP will provide its own SPF mechanism (usually an include statement). It's crucial to combine these into a single SPF record for the subdomain, ensuring you don't exceed the 10 DNS lookup limit, which can cause SPF validation failures. This limit is why some SPF configurations, like certain Mailchimp setups, are not recommended to be directly included. You can read more about why you shouldn't add Mailchimp to your SPF record directly.
Proper configuration of these records is a key component of what DNS records are needed for email sending subdomains. It also helps with the nuances of how to configure SPF when sending from a subdomain with a different 'from' email domain.
Root domain SPF record
Purpose: Authorizes mail servers for your primary domain (e.g., example.com).
Scope: Applies only to the root domain. Does not automatically cover subdomains.
Example: v=spf1 include:mainesp.com ~all
Subdomain SPF record
Purpose: Authorizes mail servers for a specific subdomain (e.g., mail.example.com).
Scope: Applies only to the subdomain it's published for. Independent of the root domain's SPF.
Example: v=spf1 include:esp-for-sub.com ~all
SPF and DMARC for subdomains
While SPF records for subdomains are distinct, it's important to consider their interaction with DMARC (Domain-based Message Authentication, Reporting, and Conformance). Unlike SPF, a DMARC record for your root domain can, by default, apply to all subdomains, unless you explicitly specify a subdomain policy using the sp tag. This difference is key for comprehensive email authentication.
Even with a DMARC policy covering subdomains, the underlying SPF record is still crucial. DMARC relies on SPF (and DKIM) to achieve alignment. If your subdomain's email fails SPF validation, it will also fail DMARC alignment, leading to the same deliverability problems as if DMARC wasn't even in place. This is part of the broader discussion on a simple guide to DMARC, SPF, and DKIM.
Therefore, even if your DMARC policy is configured to apply to subdomains, ensure that any subdomain used for sending email has its own accurately configured SPF record. This provides the necessary authentication foundation for DMARC to then enforce your policies effectively.
Authentication Protocol
Inheritance Behavior
SPF (Sender Policy Framework)
Does not automatically inherit. Each subdomain requires its own dedicated SPF record if it sends email. This is essential for proper authentication.
DMARC (Domain-based Message Authentication, Reporting, and Conformance)
Automatically applies to all subdomains by default, unless a specific sp (subdomain policy) tag is set. It relies on SPF and DKIM for validation.
Views from the trenches
Best practices
Always publish a dedicated SPF record for any subdomain you use to send email, even if your root domain has one.
Combine all required 'include' mechanisms from your email service providers into a single SPF record for each sending subdomain.
Monitor SPF alignment in your DMARC reports to identify any subdomain SPF validation failures.
Common pitfalls
Assuming SPF records for the main domain automatically apply to subdomains, leading to authentication failures.
Exceeding the 10-DNS lookup limit within an SPF record by adding too many 'include' mechanisms.
Forgetting to update the subdomain's SPF record when changing email service providers or adding new sending sources.
Expert tips
Utilize a 'p=none' DMARC policy initially to collect reports and identify all legitimate sending sources for your subdomains before enforcing stricter policies.
Consider using a dedicated subdomain for each type of email traffic (e.g., marketing.example.com, transactional.example.com) to better manage sender reputation and SPF records.
Regularly review your DNS records for all sending domains and subdomains to ensure they are current and correctly configured.
Marketer view
Marketer from Email Geeks says they always set up SPF for subdomains, going overboard on authentication to account for varied ways email servers check authentication.
2020-03-15 - Email Geeks
Expert view
Expert from Email Geeks says a subdomain absolutely needs its own SPF record because there is no concept of 'domain' or 'subdomain' inheritance in DNS itself. Unless a protocol explicitly states otherwise, you need an exact match for the record.
2020-03-15 - Email Geeks
Summary of SPF for subdomains
To sum it up, if your subdomain is actively sending emails, it requires its own, properly configured SPF record. While DMARC can offer some overarching protection for your domain and its subdomains, it doesn't replace the need for specific SPF records for each sending hostname. Ignoring this can lead to emails landing in spam, reputation damage, and potential blocklisting (or blacklisting).
Ensuring every email-sending subdomain has an accurate SPF record is a fundamental step in achieving strong email deliverability and protecting your sender reputation. It's a small effort with significant long-term benefits for your email program.
