Summary
Using subdomains for email sending offers significant advantages in managing sender reputation and segmenting email traffic. Key benefits include isolating the reputation of different mail streams (marketing vs. transactional) to prevent deliverability issues, enabling experimentation with new sending practices without risking the primary domain's reputation, and providing more granular control over authentication (SPF, DKIM). Subdomains also facilitate organizational clarity by separating email streams from different departments or sources. When implementing subdomains, consider the business needs of your organization, maintainability, and the importance of warming up new subdomains. Avoiding cousin domains is essential for brand protection. A sensible subdomain strategy is a business decision, not just a technical one and will always be needed for SPF alignment. However, sender reputation is calculated by domain and any subdomains will contribute positively or negatively towards a domain's reputation.
Key findings
- Reputation Isolation: Subdomains isolate the reputation of different email streams (marketing, transactional, etc.), preventing issues in one area from impacting others.
- Granular Control: Subdomains offer granular control over SPF and DKIM records, allowing for customized authentication policies.
- Organizational Clarity: Subdomains segment email streams from different departments or sources, improving organization and issue identification.
- Safe Experimentation: Subdomains enable experimentation with new sending practices without risking the primary domain's deliverability.
- SPF Alignment Requirement: A subdomain is always needed for SPF alignment.
Key considerations
- Business Needs: The optimal subdomain strategy depends on the specific business needs and scale of your organization.
- Maintainability: Consider the long-term maintainability and ease of use of your chosen subdomain structure.
- Warm-up: New subdomains require a gradual warm-up process to establish a positive reputation with mailbox providers.
- Cousin Domains: Avoid 'cousin domains' for branding consistency and to prevent user confusion.
- If it Works: If your deliverability is good then consider if implementing subdomains is worth it.
What email marketers say
11 marketer opinions
Using subdomains for email sending offers several benefits, primarily related to reputation management and segmentation. They allow you to isolate the impact of different types of email (marketing vs. transactional) or different sending sources (departments or providers) on your overall domain reputation. Subdomains also enable you to experiment with new sending practices or troubleshoot deliverability issues without risking your core email reputation. Remember to warm up new subdomains gradually, as with new domains. Avoiding 'cousin domains' is also important for brand protection.
Key opinions
- Reputation Isolation: Subdomains isolate the reputation of different email streams, preventing issues in one area (e.g., marketing) from affecting others (e.g., transactional).
- Experimentation: Subdomains allow safe experimentation with new sending practices without risking your primary domain's reputation.
- Segmentation: Subdomains enable the segmentation of email traffic by type (transactional, marketing) or department (sales, support), improving organization and issue identification.
- Brand protection: Cousin domains can confuse users so best to avoid these and stick to subdomains.
Key considerations
- Warm-up: New subdomains need to be warmed up gradually to build a positive reputation with mailbox providers.
- Volume: If sending large volumes, splitting into subdomains is crucial.
- Type of Mail: It's beneficial to separate transactional and marketing emails onto subdomains for deliverability.
- When to Use: If you're experiencing deliverability problems, a subdomain can isolate the issue.
Marketer view
Marketer from Email Geeks shares that sharing a domain is bad, subdomain reputation is less than a domain reputation, and subdomains should be warmed.
9 Sep 2023 - Email Geeks
Marketer view
Email marketer from SendGrid states that using subdomains can help protect your primary domain's reputation. If a subdomain's reputation is damaged due to sending practices, it won't directly impact the deliverability of emails sent from your main domain.
13 Feb 2023 - SendGrid
What the experts say
6 expert opinions
Using subdomains offers benefits for email deliverability, primarily in reputation management and organizational structure. Separating mail streams (e.g., marketing vs. transactional) helps isolate reputation impacts, preventing issues with one from affecting the other. Early decision-making is crucial for a sensible subdomain plan as your organization grows, allowing for maintainability and ease of use. SPF alignment at ESPs will always require a subdomain for bounce domains. Ultimately, there is no one-size-fits-all approach; the best strategy depends on your business needs. Think of a subdomain as a department name on an envelope, protecting other parts of your organization if deliverability issues arise.
Key opinions
- Reputation Isolation: Subdomains help separate the reputations of different mail streams, such as marketing and transactional emails.
- Strategic Planning: Making early decisions about subdomain usage creates a maintainable and easy-to-use email infrastructure.
- SPF Alignment: A subdomain is always needed for SPF alignment at ESPs (bounce domain).
- Sender Identity: Using a subdomain allows you to keep other parts of the business separate.
Key considerations
- Business Needs: The right subdomain strategy is unique to each company's specific business needs.
- Maintainability: Subdomain decisions impact maintainability and ease of use as your email program evolves.
- DKIM: Consider if you want all email streams to use your primary domain or separate subdomains for DKIM authentication.
- If it works: If your current email setup is performing well, consider the impact of changing your current setup.
Expert view
Expert from Email Geeks explains that you will always need a subdomain for SPF alignment at ESPs which is the bounce domain, and that you may also want to think about what to use in the DKIM - do you want every provider to use your primary domain for DKIM authentication or do you want marketing to have a different subdomain from support?
5 Mar 2022 - Email Geeks
Expert view
Expert from Word to the Wise explains that subdomains are useful for separating different types of mail streams and their associated reputations. For instance, separating marketing from transactional email ensures that issues with marketing campaigns don't negatively impact the deliverability of important transactional messages.
5 Apr 2022 - Word to the Wise
What the documentation says
4 technical articles
Email deliverability is enhanced by using subdomains, primarily for isolating sender reputation and gaining granular control over authentication. Google Workspace Admin Help suggests dedicated subdomains for bulk sending to protect core business email deliverability. The RFC Editor highlights the ability to specify different authentication policies (SPF/DKIM) for various email streams, a key flexibility for larger organizations. Microsoft emphasizes that sender reputation is calculated by domain, and subdomains can isolate different types of sending to prevent deliverability issues. AWS recommends separating different IP addresses for different types of email while ensuring SPF, DKIM, and DMARC are properly configured.
Key findings
- Reputation Isolation: Subdomains isolate marketing email reputation from primary domain, protecting core business email deliverability.
- Authentication Control: Subdomains allow granular control over SPF and DKIM records for different email streams.
- Sender Reputation Calculation: Sender reputation is calculated by domain, and isolating sending types onto subdomains helps manage reputation.
- IP Separation: Best practice involves separating different IP addresses for different types of email.
Key considerations
- Bulk Sending: Consider a dedicated subdomain for bulk sending.
- Organization Size: Flexibility in authentication policies is particularly important for larger organizations.
- Authentication Setup: Ensure SPF, DKIM, and DMARC are properly configured when using subdomains.
- Domain impact: Remember subdomains can still contribute positively or negatively to the main domain
Technical article
Documentation from AWS shares that in terms of best practice you should separate out different IP addresses for different types of email to prevent deliverability issues. You need to make sure you also setup SPF, DKIM and DMARC properly
2 Apr 2023 - AWS
Technical article
Documentation from Microsoft explains that sender reputation is calculated by domain, and any subdomains will contribute positively or negatively towards a domains reputation. It is best to isolate different types of sending onto different subdomains.
8 Jun 2025 - Microsoft
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