Why is my DKIM verification still showing the main domain instead of my subdomain?
Matthew Whittaker
Co-founder & CTO, Suped
Published 3 Sep 2025
Updated 11 Sep 2025
9 min read
It can be confusing when you're diligently setting up email authentication for a subdomain, only to find that the DKIM verification is still reporting your main domain. This issue, where your emails are sent from something like email@subdomain.yourcompany.com but the DKIM signature shows yourcompany.com, is a common stumbling block. It suggests that while your emails might be authenticated, they're not necessarily aligned with the subdomain you intend them to be sent from, which can impact your DMARC compliance and overall deliverability. This typically happens when the DomainKeys Identified Mail (DKIM) key used for signing doesn't match the subdomain in the From: header.
This discrepancy can occur for various reasons, ranging from incorrect DNS record setup to specific configurations (or lack thereof) within your Email Service Provider (ESP). Understanding the nuances of DKIM with subdomains is crucial for maintaining a strong sender reputation and ensuring your emails reliably reach the inbox. It's not a dumb question at all, it's a very common point of confusion for many email senders. Let's explore why this happens and how to fix it.
DomainKeys Identified Mail (DKIM) works by attaching a digital signature to your outgoing emails. This signature is generated using a private key on your sending server. The corresponding public key is published in your domain's DNS records as a TXT or CNAME record. Receiving email servers use this public key to verify that the email originated from your domain and that its content hasn't been tampered with in transit. The domain specified in the DKIM signature, known as the d= tag, is what receiving servers look at.
When you send emails from a subdomain, such as mail.yourcompany.com, the expectation is that the DKIM signature's d= tag will also reflect this subdomain for proper DMARC alignment. However, if your ESP is configured to sign with your main domain's key, or if the subdomain's DKIM records are not properly set up, the d= tag in the email header might still show your main domain. This is not necessarily a failure of DKIM authentication, but it is a failure of DKIM alignment from a DMARC perspective, which can negatively affect deliverability. This is why it's important to understand how DKIM works with subdomains.
While subdomains can inherit certain DNS records from the main domain, DKIM typically requires dedicated records. Each unique sending domain (whether it's a root domain or a subdomain) that you want to be explicitly authenticated via DKIM and aligned for DMARC, generally needs its own DKIM key pair and corresponding public key published in its specific DNS zone. If you are seeing this issue, you will need to troubleshoot why your DKIM is failing.
Why the main domain might appear in DKIM verification
The primary reason you might see your main domain in the DKIM verification for emails sent from a subdomain is a misconfiguration with your Email Service Provider (ESP) or your DNS records. Many ESPs, like Iterable or Mailgun, provide you with CNAME records to add to your DNS, which point to their own signing keys. If these CNAMEs are not correctly set up for your specific subdomain, or if the ESP itself isn't configured to use the subdomain for signing, it will default to the main domain's existing DKIM setup, or even an ESP-owned signing domain, which won't align with your desired subdomain. If you're experiencing DKIM verification failures, it's time to investigate.
Incorrect setup
Missing DNS records: No specific DKIM records (TXT or CNAME) published for the subdomain itself.
ESP configuration: Your Email Service Provider (e.g., Iterable) is not configured to sign emails with the subdomain's DKIM key.
Generic signing: The ESP might be using a generic DKIM key tied to their own sending domain or your main domain by default, leading to misalignment.
Correct setup
Dedicated DNS records: A unique DKIM record (TXT or CNAME) is published for subdomain.yourcompany.com.
ESP-specific settings: Your ESP is explicitly configured to authenticate and sign emails with the subdomain, not the main domain.
Aligned signing: The DKIM d= tag in the email header matches the subdomain in the From: header.
This problem often arises when using third-party email services that have their own default signing practices. For instance, if you're using a platform and you've verified your main domain, but then you try to send from a subdomain, the platform might still be using the root domain's key unless explicitly told otherwise. You must ensure that your ESP has the correct configurations for your subdomain to handle SPF, DKIM, and DMARC for marketing emails.
The key here is understanding that DKIM is not just about having a valid signature, but about having a signature that aligns with the domain in your email's visible From: header for DMARC. If the domains don't match, even if the signature is technically valid, your DMARC check can fail, leading to emails potentially landing in spam or being rejected altogether. This is why DKIM passes even though domains don't match, but DMARC fails.
Correctly configuring DKIM for subdomains
To ensure your DKIM verification correctly shows your subdomain, you need to follow a few critical steps. The first and most important step is to configure your ESP (such as Iterable, Mailgun, or any other sending service) to specifically use the subdomain for DKIM signing. This usually involves navigating to the domain authentication or sending domain settings within your ESP's dashboard. You'll typically find instructions there on how to add or update DNS records for your subdomains. If your ESP only allows one sending domain per account or subaccount, you may need to reach out to their support for clarification.
Setting up DKIM for your subdomain
Generate keys: Your ESP will provide you with a DKIM public key (often as a CNAME record) that needs to be published in your DNS for the specific subdomain. Do not use the same key for multiple domains, as this can lead to issues.
Publish DNS records: Add the provided DKIM records to your DNS settings for the subdomain. This is usually a CNAME record with a specific hostname (the DKIM selector, e.g., s1._domainkey.subdomain.yourcompany.com) pointing to a value provided by your ESP. Make sure to specify the subdomain clearly when adding these records.
Verify setup: After adding the records, use an online DKIM checker or your ESP's verification tool to confirm that the DKIM record for your subdomain is correctly published and valid. Tools like Google Postmaster Tools can also help you monitor your domain's authentication status.
It's common for these records to take some time to propagate across the internet, so patience is key. It might take up to 48 hours for the changes to fully reflect. Always double-check the exact CNAME or TXT values provided by your ESP. Even a small typo can prevent DKIM from verifying correctly, leading to your DKIM record not validating.
DMARC (Domain-based Message Authentication, Reporting, and Conformance) plays a critical role in email authentication by building upon SPF and DKIM. For DMARC to pass, at least one of SPF or DKIM must pass, and crucially, it must also align. DKIM alignment means that the domain in the d= tag of the DKIM signature must either be identical to, or a subdomain of, the domain in the email's visible From: header.
If you're sending from email@subdomain.yourcompany.com but your DKIM signature's d= tag is yourcompany.com, this will cause a DKIM alignment failure for DMARC. This is because the organizational domain of the From: header (which is yourcompany.com) does not strictly match the signing domain yourcompany.com if the DMARC policy is set to strict alignment, or if the system expects an exact match for the subdomain. You may need to resolve DMARC verification failures.
Implementing DMARC and monitoring your DMARC reports is essential to catch these alignment issues early. These reports provide invaluable insights into how your emails are being authenticated and handled by receiving mail servers. Suped offers the most generous free plan for DMARC monitoring, allowing you to track your email authentication status and identify sources of non-compliance, including DKIM alignment issues for subdomains. You can also use our free DMARC record generator tool to create robust policies.
By actively monitoring your DMARC reports, you can quickly spot when your DKIM records aren't aligning as expected, allowing you to make the necessary adjustments to your ESP configuration or DNS records. This proactive approach ensures that your sending reputation remains strong and your emails avoid the spam folder or being blocked by blocklists (or blacklists). Using a tool like Suped simplifies this process, providing clear insights into your email authentication performance.
Views from the trenches
Best practices
Always verify DKIM setup directly within your ESP's domain authentication settings.
Publish unique DKIM CNAME or TXT records for each subdomain you send from.
Proactively monitor your DMARC reports to identify any DKIM alignment issues.
Common pitfalls
Assuming DKIM setup for the main domain automatically covers all subdomains.
Forgetting to configure the ESP to use the subdomain's DKIM keys for signing.
Typos in DKIM DNS records, preventing proper verification.
Expert tips
Using a dedicated email testing tool can provide immediate feedback on DKIM and DMARC alignment.
Regularly review your DNS records to ensure they are up-to-date and correctly configured.
Implement a DMARC 'p=none' policy initially to gather data before enforcing stricter policies.
Expert view
An expert from Email Geeks says that if you haven't published a specific DKIM key for the subdomain, then you haven't correctly set up the signing for it.
2024-09-03 - Email Geeks
Expert view
An expert from Email Geeks suggests that you must configure your Email Service Provider to sign with the subdomain and publish a corresponding DKIM public key in your DNS records.
2024-09-03 - Email Geeks
Ensuring proper DKIM for your subdomains
Correct DKIM verification for subdomains is vital for maintaining email deliverability and DMARC compliance. The key takeaway is that each subdomain you use for sending emails needs its own explicit DKIM configuration, both in your DNS records and within your Email Service Provider. Simply setting up DKIM for your main domain is not enough to ensure proper alignment when sending from a subdomain. By carefully following the setup instructions provided by your ESP and ensuring the correct DNS records are published for each subdomain, you can resolve these alignment issues. Remember to leverage DMARC reporting tools, such as Suped's DMARC monitoring platform, to gain visibility into your email authentication status and quickly address any discrepancies.
Proactive management of your DKIM records and consistent monitoring of your email authentication with a reliable platform like Suped will ensure your emails are always verified against the correct domain, building trust with recipients and improving your overall email program's success. Don't let a small configuration oversight lead to major deliverability problems.
