What checklist of things to check when switching from sending emails from a primary domain to a subdomain?

Summary

When transitioning email sending from a primary domain to a subdomain, a multi-faceted approach is essential for maintaining deliverability. This includes technical configurations, reputation building, and content optimization. Core technical steps are updating SPF, DKIM, and DMARC records to authenticate the new subdomain, verifying reverse DNS records, and configuring the subdomain within the email sending platform. Simultaneously, building a positive reputation involves warming up the subdomain by gradually increasing sending volume, and possibly using a second DKIM signature for accelerated learning by mailbox providers. Proactive reputation monitoring using tools like Google Postmaster Tools is critical. Segmenting email streams onto distinct subdomains (if appropriate) to maintain deliverability by isolating any email type is also a consideration. Further, maintain good list hygiene, optimize email content to avoid spam triggers, test rendering, encourage subscriber engagement, and establish feedback loops with email providers.

Key findings

  • DNS Authentication: Update SPF, DKIM, and DMARC records for the subdomain.
  • Reputation Building: Warmup the subdomain gradually and monitor its reputation.
  • Subdomain Configuration: Properly configure the subdomain within your email sending platform.
  • Email Stream Separation: Consider using separate subdomains for different email streams.
  • List Hygiene: Maintain a clean email list for deliverability.
  • Content Optimization: Optimize email content to avoid spam triggers.
  • DKIM Signing Order: DKIM signing order can influence sender reputation.
  • IP Warmup: If the IP changes, implement a proper IP warmup strategy.
  • PTR Record: Verify the reverse DNS record is properly configured.
  • HELO domain Considerations: Appropriate decision about HELO domain may be needed.

Key considerations

  • Phased Implementation: Implement changes in phases to monitor deliverability impact.
  • Proactive Monitoring: Continuously monitor sender reputation using available tools.
  • Sender Platform Settings: Ensure subdomain settings and authentication are accurate on your sending platform.
  • Content Scrutiny: Regularly review email content for spam triggers and best practices.
  • List Management: Implement strategies for list cleaning and validation.
  • Feedback Loops: Set up feedback loops to monitor spam complaints.
  • Authentication Verification: Validate SPF, DKIM, and DMARC records using a checker.
  • Adaptability: Be prepared to adapt strategies based on monitoring and feedback.
  • HELO Domain: Assess whether the HELO domain should be changed or kept the same.

What email marketers say
10Marketer opinions

When switching from a primary domain to a subdomain for email sending, a comprehensive checklist should be followed to maintain or improve deliverability. Key areas include warming up the new subdomain by gradually increasing email volume, diligently monitoring sender reputation metrics (bounce rates, spam complaints), and ensuring proper configuration of DNS records (SPF, DKIM, DMARC). Implementing IP warmup if the IP address is also changing, setting up feedback loops with major email providers, maintaining good email list hygiene, optimizing email content, and testing email rendering across various platforms are also crucial. Furthermore, engaging subscribers through relevant content and clear calls-to-action is essential for long-term deliverability success. Separating email streams by subdomain, if applicable, helps maintain sender reputation by isolating potential deliverability problems.

Key opinions

  • Subdomain Warmup: Gradually increase email volume to establish a positive reputation.
  • Reputation Monitoring: Continuously monitor sender reputation and deliverability metrics.
  • DNS Configuration: Verify SPF, DKIM, and DMARC records for the subdomain.
  • IP Warmup (if applicable): Implement IP warmup alongside subdomain warmup when changing IPs.
  • Feedback Loops: Set up feedback loops with major email providers to monitor spam complaints.
  • List Hygiene: Maintain good email list hygiene by removing inactive subscribers.
  • Content Optimization: Optimize email content to avoid spam triggers.
  • Email Testing: Test email rendering across different email clients.
  • Subscriber Engagement: Focus on engaging subscribers with relevant content.
  • Subdomain Separation: Consider using separate subdomains for different email streams to help prevent deliverability problems.

Key considerations

  • Gradual Warmup: Avoid sudden spikes in sending volume to prevent deliverability issues.
  • Proactive Monitoring: Regularly monitor sender reputation and take prompt action to address problems.
  • Authentication: Ensure SPF, DKIM, and DMARC are correctly configured to authenticate emails.
  • Email Content: Pay close attention to email content and structure to prevent spam classification.
  • List Maintenance: Regularly clean your email list to improve engagement and reduce bounce rates.
  • Test and Validate: Thoroughly test and validate configurations before fully transitioning to the subdomain.
  • Segment Streams: Segment email streams onto different subdomains based on email type for maintainability.
Marketer view

Email marketer from Litmus says to use a DNS record checker to verify that your SPF, DKIM, and DMARC records are correctly configured for the subdomain. This ensures that your email authentication settings are properly implemented and can help prevent deliverability issues.

September 2021 - Litmus
Marketer view

Email marketer from Email Geeks says it's a good idea to make it obvious what the stream is for by using separate subdomains.

August 2021 - Email Geeks
Marketer view

Email marketer from SendGrid explains that focus on engaging your subscribers by sending relevant and valuable content. Encourage recipients to interact with your emails by including clear calls-to-action and providing opportunities for feedback. High engagement rates can improve your sender reputation and deliverability.

May 2023 - SendGrid
Marketer view

Email marketer from Mailjet explains that warming up the subdomain is critical. Start by sending low volumes of email and gradually increase over time. Monitor your sender reputation and deliverability metrics closely during the warmup period to identify and address any issues promptly. This allows mailbox providers to learn the legitimacy of the new subdomain.

October 2021 - Mailjet
Marketer view

Email marketer from Quora shares the advice to maintain good email list hygiene by regularly removing inactive subscribers and validating email addresses. This helps reduce bounce rates and improve overall deliverability, ensuring that your emails reach engaged recipients.

June 2021 - Quora
Marketer view

Email marketer from GMass recommends sending test emails to different email providers (Gmail, Yahoo, Outlook, etc.) to check for deliverability issues and rendering problems. Analyze the headers of the test emails to identify any potential authentication or configuration issues. The URL explains more about GMass services.

September 2022 - GMass
Marketer view

Email marketer from Email On Acid answers says to review your email content to ensure it complies with email marketing best practices and avoids spam triggers. Optimize subject lines, body copy, and images to improve engagement and reduce the likelihood of being flagged as spam. Test your email rendering to ensure it displays properly across different email clients and devices.

November 2023 - Email On Acid
Marketer view

Email marketer from Reddit explains that if you are also changing your IP address, implement a proper IP warmup strategy alongside the subdomain warmup. Gradually increase sending volume from the new IP address to establish a positive reputation with mailbox providers. If you are not changing your IP, this can be skipped.

August 2022 - Reddit
Marketer view

Email marketer from StackOverflow recommends setting up feedback loops with major mailbox providers like Gmail, Yahoo, and Outlook. This allows you to receive notifications about spam complaints, enabling you to promptly address any issues and maintain a positive sender reputation. This would be useful if deliverability problems are experienced.

July 2022 - StackOverflow
Marketer view

Email marketer from SparkPost explains that continuously monitor your sender reputation and deliverability metrics using tools like Google Postmaster Tools and Sender Score. Pay attention to bounce rates, spam complaints, and engagement metrics to identify and address any deliverability issues proactively. The URL provides information on SparkPost's services.

August 2021 - SparkPost

What the experts say
5Expert opinions

When transitioning email sending from a primary domain to a subdomain, several factors are critical for maintaining deliverability. Warming up the subdomain is essential, which can be accelerated by using a secondary DKIM signature to introduce the new domain to machine learning filters. Separating subdomains for different email types might be beneficial depending on volume and deliverability risks. It's crucial to properly configure the subdomain within the email sending platform, ensuring all authentication settings are in place. DKIM signing order matters, influencing how ISPs assess reputation. Finally, different approaches to subdomain setup might be needed based on specific scenarios, including decisions about changing the HELO domain.

Key opinions

  • Subdomain Warmup: Warming up the subdomain is essential for positive reputation with mailbox providers.
  • Secondary DKIM Signature: Adding a secondary DKIM signature can accelerate the subdomain warmup process.
  • Subdomain Separation: Separate subdomains are useful for different email streams but not always necessary.
  • Proper Configuration: Ensuring the subdomain is correctly configured within the email sending platform is crucial.
  • DKIM Signing Order: DKIM signing order impacts how ISPs assess reputation.
  • HELO Domain Considerations: Different HELO domain approaches may be necessary for influencing sender reputation based on the situation.

Key considerations

  • Warmup Strategy: Determine the appropriate warmup strategy, considering using a secondary DKIM signature.
  • Volume and Deliverability: Assess email volume and deliverability concerns when deciding to separate subdomains.
  • Platform Configuration: Ensure all necessary authentication settings are in place within the email sending platform.
  • Signing Order: Strategically manage the DKIM signing order to optimize reputation benefits.
  • HELO Settings: Assess whether the HELO domain should be changed or kept the same, as it influences sending reputation.
Expert view

Expert from Spam Resource explains that when switching to a subdomain, it is crucial to ensure that the subdomain is properly configured within your email sending platform. Verify that the subdomain is correctly set up for sending emails and that all necessary configurations, such as authentication settings, are in place. Check that your email sending platform recognizes the new subdomain and can send emails on its behalf.

October 2022 - Spam Resource
Expert view

Expert from Email Geeks explains DKIM signing order. In header order (top down as reading headers): known signature then new signature. In signing order (so as you sign the outbound message): new signature than known signature. After a while you can switch them so it’s (header order) new signature then known signature. Then you can drop the old signature.

March 2025 - Email Geeks
Expert view

Expert from Word to the Wise shares the advice that they recommend different approaches to subdomains depending on the specific situation. She talks through when it's useful to change the HELO domain and when to keep it the same and how these decisions can influence sending reputation.

July 2022 - Word to the Wise
Expert view

Expert from Email Geeks explains that you need to warmup the subdomain, but it doesn’t have to be a long warmup. They suggest adding a second DKIM signature with the domain to warmup for a while to introduce the domain and get the machine learning filters used to seeing it before it’s the identity that reputation is hung off of.

September 2024 - Email Geeks
Expert view

Expert from Email Geeks says that in general separate subdomains is preferred, but in some cases it’s not really necessary, it depends on volumes and deliverability concerns.

September 2024 - Email Geeks

What the documentation says
4Technical articles

When transitioning email sending from a primary domain to a subdomain, it is essential to update DNS records to ensure proper authentication and deliverability. This includes updating SPF records to authorize the subdomain's sending sources, generating and publishing a new DKIM record for the subdomain to sign emails correctly, updating the DMARC record to align with sending practices, and verifying that the reverse DNS (PTR) record is properly configured and matches the hostname of the sending server.

Key findings

  • SPF Record Update: SPF records must be updated to include the subdomain as an authorized sending source.
  • DKIM Record Generation: A new DKIM record should be generated and published for the subdomain.
  • DMARC Record Update: DMARC record needs to be updated to include the subdomain, ensuring policy alignment.
  • Reverse DNS (PTR) Record Verification: Verify the reverse DNS record is properly configured and matches the sending server's hostname.

Key considerations

  • Accurate SPF Configuration: Ensure the SPF record accurately reflects all sending sources for the subdomain.
  • DKIM Key Validation: Validate the DKIM configuration to confirm emails are signed correctly.
  • DMARC Policy Alignment: Ensure the DMARC policy aligns with sending practices for the subdomain.
  • Hostname Matching: Confirm that the PTR record matches the sending server's hostname to establish trust.
Technical article

Documentation from Google Workspace Admin Help explains that you need to update your SPF records to include the subdomain. This involves adding the subdomain to the existing SPF record or creating a new SPF record specifically for the subdomain. Ensure the SPF record accurately reflects the sending sources for the subdomain to avoid deliverability issues. The URL provided explains more on using SPF records.

March 2024 - Google Workspace Admin Help
Technical article

Documentation from RFC standard explains that verify that your reverse DNS (PTR) record is properly configured for the sending IP address. The PTR record should match the hostname of your sending server, helping to establish trust with email receivers. More information on reverse DNS can be found via the link.

April 2022 - RFC-Editor
Technical article

Documentation from Microsoft 365 documentation explains that when switching to a subdomain, generate a new DKIM record for the subdomain and publish it in the subdomain's DNS settings. Ensure that the sending server is configured to sign emails using the new DKIM key. Validate the DKIM configuration to confirm that emails are being signed correctly. The URL provides information on DKIM.

December 2024 - Microsoft 365 documentation
Technical article

Documentation from DMARC.org explains that update your DMARC record to include the subdomain. This might involve creating a separate DMARC record for the subdomain or modifying the existing one to cover the new sending domain. Ensure the DMARC policy aligns with your sending practices for the subdomain, specifying how email receivers should handle emails that fail SPF and DKIM checks. See URL to learn more about DMARC.

December 2022 - DMARC.org