What checklist of things to check when switching from sending emails from a primary domain to a subdomain?
Matthew Whittaker
Co-founder & CTO, Suped
Published 25 Jun 2025
Updated 19 Aug 2025
7 min read
Shifting email sending from your primary domain to a subdomain is a strategic move many organizations consider to manage sender reputation, segment email types, or isolate risks. While it sounds straightforward, it involves more than just updating SPF, DKIM, and DMARC records. A methodical approach is essential to ensure a smooth transition and maintain strong email deliverability.
This checklist outlines key steps and considerations, helping you navigate the complexities of moving your email infrastructure without compromising your inbox placement. It’s about being proactive and setting up your new subdomain for long-term success.
Technical DNS checklist
Before you begin sending from your new subdomain, it is crucial to configure all necessary DNS records. These records are the backbone of email authentication and play a significant role in how mailbox providers assess your sender legitimacy. Incorrect or missing records can lead to immediate deliverability issues, including emails landing in spam folders or being rejected outright.
Even though you are moving to a subdomain, you should treat it almost like a new sending entity regarding DNS setup. This ensures that the subdomain has its own, distinct authentication signals, preventing any negative reputation from the primary domain from carrying over, and vice-versa.
SPF record: Create a new SPF record specifically for your subdomain. It should include all authorized sending IP addresses and third-party email service providers (ESPs) that will send mail on behalf of this subdomain. Remember to not exceed the 10-lookup limit.
DKIM record: Configure DKIM signatures for your subdomain. You'll typically get these from your ESP. Each subdomain requires its own DKIM key pair and DNS entry, such as selector1._domainkey.sub.yourdomain.com.
DMARC record: Implement a DMARC policy specifically for the subdomain. Start with a p=none policy to monitor activity before moving to quarantine or reject. This is critical for visibility into authentication failures.
MX records: If you intend to receive replies or inbound mail to addresses on the subdomain, ensure proper MX records are set up for it. Even if not, some verification processes may require an MX record.
A records/Redirects: Confirm any necessary A records or redirects are in place, especially if your sending subdomain links back to web content or landing pages related to your primary domain.
Example SPF Record for a SubdomainDNS
v=spf1 include:spf.your-esp.com ~all
sub.yourdomain.com. IN TXT "v=spf1 include:spf.your-esp.com ~all"
This granular control over DNS records for your subdomain ensures that its email traffic is evaluated independently, helping to protect your primary domain's reputation from the activities of your subdomain, and vice-versa.
Sender reputation and warm-up
Even though you are maintaining the same root domain, a new subdomain has its own, distinct sender reputation. This means you will need to warm up the subdomain, just like a new IP address or a completely new domain. Skipping this step can lead to poor inbox placement, as mailbox providers (ISPs) will be wary of sudden, high-volume sending from an unfamiliar sender.
Gradual ramp-up: Start with low volumes of highly engaged recipients and gradually increase your sending volume over several days or weeks. This helps ISPs build trust in your new sending identity. You can find more details on how to warm up a subdomain in our dedicated guide.
Monitor performance: Pay close attention to deliverability metrics, including open rates, click-through rates, bounce rates, and spam complaints. These indicators will tell you how well your new subdomain is being received. Use tools like Google Postmaster Tools to track domain reputation and identify potential issues.
The length of the warm-up period can vary. While a brand new domain might require months, a subdomain often needs a shorter period, perhaps a week or two, for machine learning filters to recognize its legitimacy. However, consistency and careful monitoring remain key.
An interesting strategy is to use dual DKIM signatures during the warm-up. You can maintain your existing, trusted DKIM signature while simultaneously adding a new DKIM signature for the subdomain. This helps gradually introduce the new subdomain’s identity to mailbox providers without immediately risking your established reputation. Once the new subdomain builds its own trust, the old signature can be phased out.
Strategic separation of email streams
One of the primary reasons for switching to a subdomain is to segment your email traffic. Different types of emails, such as marketing campaigns versus transactional messages, have different sending patterns and deliverability expectations. By separating them onto different subdomains, you can protect the deliverability of your critical transactional emails from potential issues with promotional content.
For instance, if your marketing emails experience a sudden spike in complaints or bounces, only the reputation of the marketing subdomain will be affected, leaving your transactional subdomain untouched. This isolation is a robust way to future-proof your email program against unforeseen deliverability challenges.
Risk: Higher risk of spam complaints, blocklisting (or blacklisting), and lower engagement.
Example subdomain: marketing.yourdomain.com
Transactional emails
Purpose: Order confirmations, password resets, shipping updates, account notifications.
Volume: Often lower volume but critical, triggered by user actions.
Risk: Low risk, high engagement expected, crucial for user experience.
Example subdomain: notifications.yourdomain.com
This segregation allows you to maintain different sender reputations for each stream, optimizing deliverability for each type of mail. It is a recommended best practice by many email deliverability experts, particularly for high-volume senders or those with mixed email content.
Ongoing verification and monitoring
Once your subdomain is configured and you have started the warm-up process, continuous verification and monitoring are paramount. This involves regular checks to ensure your DNS records are correctly resolving and that your emails are reaching the inbox, not the spam folder.
Gmail ‘Show original’: Send a test email to a Gmail account and use the “Show original” option to verify that SPF, DKIM, and DMARC all pass. This is a quick and effective way to confirm your basic authentication is correctly set up.
DMARC reports: Regularly review your DMARC aggregate and forensic reports. These reports provide invaluable insights into your email authentication status, sources sending mail on your behalf, and any potential issues with alignment or spoofing.
Blocklist monitoring: Keep an eye on major email blocklists (blacklists) to ensure your new subdomain's IP or domain isn't listed. Being on a blocklist can severely impact deliverability. You can use a blocklist checker to periodically check.
Consistent monitoring helps you quickly identify and address any issues that may arise, safeguarding your sender reputation and ensuring your emails reach their intended recipients.
Views from the trenches
Best practices
Always include MX records for your subdomain, even if you don't plan to receive mail, as some verification processes require them.
Utilize dual DKIM signatures during the transition period to gradually build reputation for the new subdomain without impacting the old one. The existing signature should be added first in the header order, followed by the new one.
Separate promotional and transactional email streams onto different subdomains to isolate potential reputation risks and optimize deliverability for each.
Regularly monitor your DMARC reports for comprehensive insights into authentication, alignment, and sending sources.
Common pitfalls
Forgetting to set up all necessary DNS records (SPF, DKIM, DMARC, MX) specifically for the new subdomain, leading to authentication failures.
Skipping the warm-up process for the subdomain, which can cause emails to be flagged as spam or rejected by mailbox providers.
Failing to monitor email deliverability metrics and DMARC reports, missing early signs of reputation issues.
Not considering the volume and type of email traffic when deciding on subdomain separation, potentially creating unnecessary complexity.
Expert tips
Consider that different receivers (ISPs) may aggregate domain reputation differently, sometimes up to the Top-Level Domain (TLD), sometimes at the subdomain level.
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Marketer view
Marketer from Email Geeks says that domain warm-up, A records or appropriate redirects, and MX records should be on your checklist when switching to a subdomain.
2021-06-28 - Email Geeks
Marketer view
Marketer from Email Geeks says that the need for a months-long warm-up depends on where you are sending, as some receivers aggregate up to the Top-Level Domain (TLD) while others do not.
2021-06-28 - Email Geeks
Ensuring a seamless email transition
Migrating email sending from a primary domain to a subdomain is a proactive step that can significantly improve your email deliverability and sender reputation management. By meticulously handling DNS configurations, dedicating time to warm up the new subdomain, strategically separating your email streams, and consistently monitoring your performance, you set yourself up for long-term success.
This structured approach helps ensure that your emails continue to reach the inbox reliably, protecting your brand's communication channels and overall email program health.
Gmail account and use the “Show original” option to verify that SPF, DKIM, and DMARC all pass. This is a quick and effective way to confirm your basic authentication is correctly set up.
