What is the best DMARC, DKIM, and SPF setup for marketing and transactional emails sent from different subdomains?
Michael Ko
Co-founder & CEO, Suped
Published 5 May 2025
Updated 18 Aug 2025
10 min read
Managing email deliverability can be complex, especially when you're sending different types of emails from various subdomains. The goal is always to ensure your messages reach the inbox, whether they're critical transactional updates or engaging marketing campaigns. Achieving this relies heavily on correctly configuring email authentication protocols, namely SPF, DKIM, and DMARC. When you segregate your email streams using subdomains, you gain more granular control over your sender reputation, but it also means each subdomain needs its own careful setup.
I've often seen organizations struggle with this, particularly with how DMARC inheritance works or ensuring SPF and DKIM are properly aligned for each sending entity. The common pitfall is treating all domains and subdomains the same way, or simply applying top-level authentication records without considering the specifics of subdomain usage. However, a tailored approach is essential for optimal performance and security.
By clearly separating your email types and authenticating them independently, you can isolate any potential reputation issues. For instance, a bounce from a marketing blast won't negatively impact the deliverability of your password reset emails. This strategic use of separate subdomains for email is a cornerstone of robust email deliverability.
The decision to use different subdomains for marketing and transactional emails is a wise one. It's a fundamental strategy for protecting your primary domain's reputation and ensuring that critical communications reliably reach their recipients. Imagine if a marketing campaign accidentally triggered a spam complaint surge, and that negatively impacted your password reset emails. This scenario is precisely what subdomains help to prevent.
Transactional emails, like order confirmations or password resets, typically have very high engagement rates and are expected by recipients. Marketing emails, while valuable, can sometimes have lower engagement or higher complaint rates, even when sent to legitimate subscribers. By separating these streams, you create distinct sending reputations for each, allowing mailbox providers to treat them differently based on their historical performance.
This isolation means that even if your marketing subdomain ends up on a blacklist or blocklist due to higher complaint rates (which can happen with legitimate marketing), your transactional emails from a different subdomain should remain unaffected. This is crucial for maintaining critical business operations that rely on reliable email delivery.
It also provides clarity in reporting. When you analyze DMARC reports or Google Postmaster Tools (or Yahoo's equivalent), you can see distinct performance metrics for each subdomain, allowing you to pinpoint issues more accurately and optimize each sending stream independently.
Core authentication protocols for subdomains
Let's dive into the specifics of setting up SPF, DKIM, and DMARC for different subdomains. It's not just about having the records, but about ensuring they are configured correctly for each specific sending context to achieve proper alignment and authentication.
SPF for subdomains
SPF (Sender Policy Framework) works by allowing a domain owner to specify which IP addresses are authorized to send email on their behalf. The key here is that SPF validation occurs against the Return-Path (also known as the Mail From or Envelope From) domain, not necessarily the From: header address. For SPF to pass DMARC alignment (relaxed or strict), the Return-Path domain must match the organizational domain of the From: header.
Therefore, for each subdomain you use for sending (e.g., m.yourdomain.com for marketing, t.yourdomain.com for transactional), you need to publish a specific SPF record for that subdomain. This record should authorize the IP addresses or sending domains of your Email Service Providers (ESPs) or mail servers used for that particular subdomain. An SPF record example might look like this:
DKIM (DomainKeys Identified Mail) provides a way to verify the authenticity of an email by digitally signing it. Unlike SPF, DKIM attaches a signature to the email header, which is then verified against a public key published in your DNS. When using subdomains, it's best practice to configure DKIM for each subdomain from which you send emails.
This means each subdomain will have its own DKIM DNS record, typically a TXT record with a selector (e.g., s1._domainkey.m.yourdomain.com). This ensures that the DKIM signature properly aligns with the From: domain, which is crucial for DMARC pass. Your ESP will provide the specific DKIM records you need to publish for each subdomain.
DMARC for subdomains
DMARC (Domain-based Message Authentication, Reporting, and Conformance) builds upon SPF and DKIM, telling receiving servers what to do with emails that fail authentication and providing valuable feedback through reports. A critical aspect of DMARC with subdomains is understanding DMARC policy placement.
By default, subdomains inherit the DMARC policy of the organizational domain. However, you can publish explicit DMARC records for subdomains using the sp (subdomain policy) tag in your main DMARC record, or by defining a separate DMARC record directly on the subdomain (e.g., _dmarc.m.yourdomain.com). The latter provides more flexibility and control over each subdomain's policy.
For Google and Yahoo's 2024 sender requirements, a p=none DMARC policy is the minimum for bulk senders, allowing you to monitor authentication failures without impacting delivery initially. Gradually moving to p=quarantine or p=reject is the ultimate goal to prevent spoofing and enhance trust.
Recommended setup by email type
When setting up DMARC, DKIM, and SPF for marketing and transactional emails on separate subdomains, the key is consistent and independent configuration for each. This ensures that each sending stream is fully authenticated and protected, preventing issues like emails landing in spam or being blocked.
SPF record: Publish an SPF record specifically for m.yourdomain.com that includes all marketing ESPs or servers. The Return-Path of your marketing emails must align with this subdomain.
DKIM record: Set up DKIM records for m.yourdomain.com, provided by your marketing ESP. This will ensure your emails are signed by the appropriate domain.
DMARC record: Publish a DMARC record directly for _dmarc.m.yourdomain.com. Start with p=none to gather reports, then move to p=quarantine or p=reject as you gain confidence. This granular control is vital for marketing email performance.
SPF record: Similar to marketing, create an SPF record for t.yourdomain.com that authorizes only your transactional email senders. Ensure the Return-Path aligns with this subdomain.
DKIM record: Publish DKIM records for t.yourdomain.com using the keys provided by your transactional ESP. This is crucial for authentication.
DMARC record: Set a DMARC record for _dmarc.t.yourdomain.com. For transactional emails, you can often move to a stricter p=quarantine or p=reject policy much faster due to their predictable nature and lower spam risk.
Monitoring and maintenance
Effective email deliverability isn't a one-time setup, it's an ongoing process of monitoring and adjustment. Once your SPF, DKIM, and DMARC records are in place for your subdomains, the work isn't over. You need to actively monitor your email performance to catch any issues early.
DMARC reports are your best friend here. They provide invaluable insight into who is sending email on behalf of your domains and subdomains, and whether those emails are passing or failing SPF and DKIM authentication. Regularly reviewing these reports allows you to identify unauthorized senders, misconfigurations, or even spoofing attempts, helping you to protect your domain reputation.
Additionally, keep an eye on your email blacklists (or blocklists). If an IP or domain associated with your sending becomes listed, it can severely impact deliverability. Proactive monitoring allows for swift action to request de-listing and address the underlying issue.
Finally, ensure that any changes to your email infrastructure or ESPs are reflected in your DNS records immediately. An outdated SPF record or a missing DKIM key can cause legitimate emails to fail authentication, leading to delivery problems. Continuous vigilance is the hallmark of strong email deliverability.
Marketing subdomain
Typically involves higher volumes, diverse recipient engagement, and a higher potential for spam complaints. Reputation management is key.
SPF: Specific SPF record for m.yourdomain.com, including marketing ESPs.
DKIM: DKIM key(s) published for m.yourdomain.com.
DMARC: Individual DMARC record for m.yourdomain.com. Start p=none, escalate carefully.
Transactional subdomain
High priority, expected emails with very low complaint rates. Deliverability must be near 100%.
SPF: Specific SPF record for t.yourdomain.com, including transactional ESPs.
DKIM: DKIM key(s) published for t.yourdomain.com.
DMARC: Individual DMARC record for t.yourdomain.com. Can often move to p=quarantine or p=reject sooner.
Views from the trenches
Getting SPF, DKIM, and DMARC right for subdomains can be tricky, but it's essential. I've heard many experiences from others in the field, and a few common themes and valuable insights emerge.
Best practices
Always publish SPF records for the exact domain used in your Return-Path, not just your main domain.
Ensure each sending subdomain has its own DKIM key pair and published public key in DNS.
Set explicit DMARC records for each subdomain, even if it mirrors the organizational domain's policy, for clarity and granular control.
Leverage DMARC reports to understand your email traffic and identify any authentication failures or unauthorized sending.
Start with a DMARC policy of p=none for monitoring, then progressively move to p=quarantine or p=reject for stronger protection.
Common pitfalls
Relying solely on a main domain's SPF record to cover all subdomains, leading to SPF alignment failures for emails sent from subdomains.
Not publishing explicit DMARC records for subdomains, leading to unintended inheritance of the main domain's policy, or no policy at all.
Exceeding the 10 DNS lookup limit for SPF records, which can cause SPF validation failures.
Failing to rotate DKIM keys periodically, which is a security best practice.
Ignoring DMARC reports, missing critical insights into email authentication issues or malicious activity.
Expert tips
Use a subdomain for each unique type of email flow (e.g., transactional, marketing, notifications, internal) to isolate sending reputation.
Continuously monitor your domain reputation with tools and services, including major mailbox providers' feedback loops and postmaster tools.
Implement MTA-STS and TLS-RPT for an added layer of security and transparency, especially for critical transactional emails.
Review your email sending setup whenever you change ESPs or add new sending platforms to ensure all authentication records are updated.
Consider using a DMARC management platform to simplify reporting and policy enforcement across multiple subdomains and sending sources.
Expert view
Expert from Email Geeks says SPF is checked against the Return-Path. The only way to achieve alignment is for the Return-Path to be in the same organizational domain as the From header.
2024-06-20 - Email Geeks
Marketer view
Marketer from Email Geeks says subdomains will inherit the DMARC policy of the main domain, unless an explicit DMARC record has been published for those specific subdomains.
2024-06-20 - Email Geeks
Final thoughts on email authentication
Setting up SPF, DKIM, and DMARC for marketing and transactional emails on different subdomains is a best practice that significantly enhances your email deliverability and security. It allows for independent reputation management, ensuring that issues with one type of email don't impact the other, and strengthens your overall email authentication posture.
The critical takeaway is to treat each subdomain as a distinct sending entity, requiring its own dedicated and correctly configured SPF, DKIM, and DMARC records. Avoid relying solely on your main domain's records, as this can lead to authentication failures and reduced inbox placement. Regularly monitoring your DMARC reports and staying vigilant about your DNS configurations will be key to long-term success.
By following these guidelines, you'll not only comply with evolving industry standards (like those from Microsoft and other major providers) but also significantly improve your chances of reaching the inbox with every message, whether it's a promotional offer or a crucial transaction confirmation.
Microsoft and other major providers) but also significantly improve your chances of reaching the inbox with every message, whether it's a promotional offer or a crucial transaction confirmation.
