Summary
While technically feasible, experts, marketers, and documentation sources largely advise against using the same subdomain for multiple email sending platforms. Concerns revolve around deliverability issues, sender reputation, and the complexities of managing authentication (SPF, DKIM, DMARC) and bounce handling. Using dedicated subdomains for each platform or type of email traffic is generally recommended for better control, isolation, and reputation management.
Key findings
- Reputation Risk: Sharing a subdomain exposes your sender reputation to the sending practices of all platforms using it; poor practices on one can negatively impact all.
- Authentication Complexity: Managing SPF, DKIM, and DMARC records becomes significantly more complex when multiple sending platforms share a subdomain.
- SPF Limits: SPF record limitations on DNS lookups can make it difficult to authorize multiple third-party senders on a single subdomain.
- Bounce Handling: Bounce handling becomes more complex, requiring a clear process to ensure bounces are correctly suppressed on the relevant sending server.
Key considerations
- Dedicated Subdomains: Consider using dedicated sending domains or subdomains for each email stream (e.g., transactional vs. marketing) or platform.
- Isolate Testing: Use separate subdomains for testing email campaigns to avoid impacting your primary sending domain's reputation.
- Careful Configuration: If sharing a subdomain, meticulously manage SPF, DKIM, and DMARC records, and actively monitor the reputation of each platform.
- DMARC Alignment: Ensure proper SPF and DKIM alignment for DMARC to pass when using different ESPs, which can be complicated on a shared subdomain.
What email marketers say
10 marketer opinions
While technically possible to use the same subdomain for multiple email sending platforms, it's generally not recommended. Doing so can lead to deliverability issues and negatively impact your sender reputation. Each platform should ideally have its own dedicated subdomain to isolate potential problems and maintain better control over authentication and reputation.
Key opinions
- Authentication Complexity: Using the same subdomain requires careful management of CNAME, TXT, SPF, and DKIM records, which can become complex when using multiple platforms.
- Reputation Risk: Sharing a subdomain means that the sending practices of one platform can affect the reputation of all platforms using the same subdomain.
- Deliverability Impact: Poor sending practices on one platform can negatively impact the deliverability of emails sent from other platforms sharing the same subdomain.
- Best Practice Recommendation: It is generally recommended to use dedicated sending subdomains for each email stream or platform to protect sender reputation.
Key considerations
- SPF Record Limits: Consider the limitations of SPF records when authorizing multiple third-party senders on a single domain or subdomain.
- DMARC Alignment: Ensure proper SPF and DKIM alignment for DMARC to pass when using multiple ESPs, which can be complicated by using a shared subdomain.
- Testing Environments: Use separate subdomains for testing purposes to avoid negatively impacting the reputation of your primary sending domain.
- Monitoring and Management: If sharing a subdomain, actively monitor and manage the reputation for each platform.
- Email Type Separation: Consider separating different types of email (e.g., transactional vs. marketing) onto separate subdomains.
Marketer view
Email marketer from Email on Acid mentions it's best to use a separate subdomain for testing various email campaigns, especially when involving different email platforms. This is to ensure that your main sending domain's reputation remains untainted during the testing phase.
21 Dec 2023 - Email on Acid
Marketer view
Email marketer from Mailjet responds that sharing a subdomain across multiple ESPs can negatively affect your sender reputation if one ESP has poor sending practices. Isolating each ESP with its own subdomain is a safer approach.
9 Nov 2022 - Mailjet
What the experts say
5 expert opinions
Experts generally advise against using the same subdomain for multiple email sending platforms due to concerns about bounce handling, sender reputation, and potential configuration errors. Setting up separate subdomains is considered best practice for isolating sending streams, protecting reputation, and managing deliverability. While it involves creating the domain and setting up DNS records, the benefits outweigh the complexity and potential risks of sharing a subdomain.
Key opinions
- Bounce Handling: Managing bounces becomes more complex when using multiple platforms on a single subdomain. A clear process is needed to ensure bounces are correctly handled and suppressed on the relevant sending server.
- Sender Reputation: Sender reputation is tied to the domain and can be negatively affected if one platform has poor sending practices. Separate subdomains help maintain individual reputations.
- Potential Configuration Errors: Sharing subdomains increases the risk of misconfiguration and potential deliverability problems.
- Complexity vs. Effort: The overhead of ensuring proper configuration and management when sharing a subdomain outweighs the effort required to set up separate subdomains.
Key considerations
- Dedicated Infrastructure: Consider setting up independent subdomains for each vendor or type of email to isolate sending streams.
- Simplified Setup: Setting up a new subdomain primarily involves creating the domain and configuring DNS records.
- Email Stream Separation: Use subdomains to separate different email streams, such as marketing versus transactional emails.
- Reputation Isolation: Separate subdomains help to isolate and protect your overall reputation, especially when one platform is new or less reliable.
Expert view
Expert from Email Geeks explains that it is poor practice to share subdomains across different mailing companies because of the high chance of messing something up, and that the overhead to prevent this is more than setting up an independent subdomain for each vendor.
18 Mar 2025 - Email Geeks
Expert view
Expert from Word to the Wise responds that sender reputation is tied to the domain, and that it is advisable to separate sending based on the type of mail you are sending. Using different subdomains for each can help maintain good reputations of the individual subdomain.
26 Jul 2021 - Word to the Wise
What the documentation says
5 technical articles
Technical documentation from RFC, DMARC.org, Google Workspace, Microsoft, and AWS recommends against using the same subdomain for multiple email sending platforms. SPF record limitations, DMARC alignment complexities, and the need for authentication (SPF and DKIM) are primary concerns. Using unique subdomains provides better control over authentication configurations, facilitates easier monitoring, and helps manage reputation and deliverability for different types of email traffic, especially when using multiple ESPs.
Key findings
- SPF Lookup Limits: SPF records have limitations on the number of DNS lookups, making it challenging to authorize multiple third-party senders on a single subdomain.
- DMARC Complications: Using different ESPs on the same subdomain can complicate DMARC alignment, as proper SPF and DKIM alignment is crucial for DMARC to pass.
- Authentication Requirements: Bulk senders should authenticate their email with SPF and DKIM, which is more manageable with separate subdomains.
- Control and Monitoring: Unique subdomains provide more control over authentication configurations and facilitate easier monitoring.
Key considerations
- Email Type Separation: Configure unique subdomains for different types of email traffic, such as separating transactional email from marketing communications.
- Authentication Practices: Ensure proper SPF and DKIM configuration for each subdomain to maintain optimal deliverability.
- DMARC Policy Inheritance: Understand that subdomains can inherit the DMARC policy of the parent domain, requiring careful alignment for DMARC compliance.
- ESP Specific Configuration: Using unique subdomains will help to create different configurations to suit each ESP.
Technical article
Documentation from RFC explains that SPF records have limitations on the number of DNS lookups, making it difficult to authorize multiple third-party senders on a single domain or subdomain without exceeding these limits.
21 May 2024 - RFC
Technical article
Documentation from Google Workspace advises that bulk senders should authenticate their email with SPF and DKIM. Using separate subdomains for different types of email can help manage reputation and deliverability.
24 Jan 2023 - Google Workspace
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