Summary
For organizations leveraging multiple email sending tools or managing diverse email streams, using unique subdomains for each service or mail type is widely considered a crucial best practice. This approach effectively isolates sender reputation, simplifying DNS management and preventing deliverability issues from one stream, such as marketing emails, from negatively impacting more critical communications like transactional notifications. While technically possible to share a subdomain with proper authentication, the associated risks and complexities generally outweigh any perceived benefits.
Key findings
- Separate Subdomains Recommended: The overwhelming consensus among email deliverability experts and major ESPs is to use a unique subdomain for each email sending tool or distinct email stream, like marketing or transactional.
- Reputation Isolation is Key: Using separate subdomains effectively compartmentalizes sender reputation, ensuring that deliverability issues, such as high bounce rates or spam complaints from one email type or tool, do not negatively affect the reputation and deliverability of others.
- Simplified Management: Unique subdomains simplify the management of DNS records, including SPF and DKIM, for each sending service, making troubleshooting and performance tracking more straightforward.
- Authentication Must Be Precise: When using multiple tools, each subdomain must have its SPF and DKIM records correctly configured to authorize the respective sending service, preventing authentication conflicts and enhancing deliverability.
- Shared Subdomain Risks: Sharing a single subdomain across multiple tools can lead to technical complexities, such as SPF record limitations and potential DKIM selector collisions, and significantly increases the risk of one tool's poor performance impacting the deliverability of all others.
Key considerations
- DNS Record Limits: Using subdomains can help address potential SPF record limitations, such as the 'too many DNS lookups' issue, by segmenting authentication records for different services.
- MX Record Constraints: A primary technical limitation for sharing a subdomain is that an MX record can only point to a single destination, primarily affecting the ability to receive mail for multiple tools on the same subdomain.
- CNAME for Authentication: Some experts recommend CNAME authentication, which creates a unique subdomain for authorization specific to an application, potentially simplifying DNS record management.
- Contextual Sharing Decisions: While generally discouraged, the decision to share a subdomain is highly contextual, though the complexities and reputation risks typically make it an unfavorable choice for most mailstreams.
- Consult IT for DNS: It is advisable to consult with your IT department or DNS administrator to confirm the specific requirements and best practices for setting up authentication records for multiple sending tools.
What email marketers say
14 marketer opinions
When managing email deliverability across multiple sending tools or distinct email streams, a strategic approach to subdomain usage is paramount. Industry experts widely advise employing unique subdomains for each separate email type, such as marketing, transactional, or notification emails, or for each different sending platform. This method is considered a best practice because it effectively isolates sender reputation, safeguarding critical email deliverability from potential issues in other, less sensitive streams. While technically feasible to configure a single subdomain for multiple senders, the inherent complexities in DNS management and the significant risk of cross-contamination of sender reputation generally make it an undesirable choice.
Key opinions
- Unique Subdomains for Each Stream: The prevailing recommendation is to assign a unique subdomain to each email sending tool or distinct email stream, such as marketing or transactional, to optimize deliverability.
- Reputation Compartmentalization: Using separate subdomains is crucial for isolating sender reputation, ensuring that deliverability challenges in one email type do not negatively affect others, thus protecting vital communications.
- Streamlined DNS Configuration: Unique subdomains allow for clear and distinct SPF, DKIM, and DMARC records for each sending service, simplifying setup, management, and troubleshooting of authentication.
- Shared Subdomain Risks: Attempting to share a single subdomain across multiple sending tools introduces significant technical complexities, such as SPF record limitations and potential DKIM conflicts, and carries a high risk of reputation damage across all associated mailstreams.
- Protection of Primary Domain: Employing dedicated subdomains for email sending helps preserve the reputation of the main website domain by clearly delineating email origin and isolating any potential deliverability issues.
Key considerations
- MX Record Limitations: A primary technical constraint for sharing subdomains is that an MX record can only point to a single destination, which complicates receiving mail for multiple tools on a shared subdomain.
- SPF Lookup Management: Subdomains are an effective strategy to mitigate potential 'too many DNS lookups' issues within SPF records by segmenting authorization for different sending services.
- Context-Dependent Decisions: While generally discouraged, the decision to share a subdomain might be considered in highly specific contexts, though the substantial risks to deliverability and reputation usually outweigh any perceived benefits.
- Comprehensive Authentication: Regardless of subdomain strategy, precise configuration of SPF and DKIM records is essential to authorize all sending IPs and domains, ensuring proper email authentication.
Marketer view
Marketer from Email Geeks explains that technically, one subdomain can send from multiple tools, but cannot receive mail for multiple tools. He adds that whether one should share subdomains is contextual, suggesting that for mailstreams using multiple tools, separating subdomains by mailstream might be an option, though mailstreams often align with individual tools anyway.
21 May 2023 - Email Geeks
Marketer view
Marketer from Email Geeks explains that it is certainly possible to use one subdomain across multiple tools, provided that authentication, such as SPF records permitting mailing from the tools' IP addresses and correctly set up DKIM, accounts for this configuration.
30 Jan 2024 - Email Geeks
What the experts say
3 expert opinions
In the realm of email deliverability, a consistent recommendation emerges regarding subdomain strategy for organizations utilizing multiple sending tools: employing unique subdomains for each platform is the established best practice. This approach is paramount for effective reputation management and ensures that deliverability issues arising from one email stream do not adversely affect others. Experts emphasize that sharing subdomains across tools is not recommended due to increased difficulty in diagnosing problems and the risk of poor performance from one sender contaminating the reputation of others.
Key opinions
- Unique Subdomain Standard: It is generally not a best practice to use the same subdomain across multiple email sending tools or ESPs; unique subdomains are strongly recommended for each.
- Isolating Sender Reputation: Employing unique subdomains for each sending tool or email stream is crucial for managing and isolating sender reputation, preventing deliverability issues from one source from affecting others.
- Preventing Cross-Contamination: Sharing a subdomain risks allowing poor performance from one Email Service Provider to negatively impact the sending reputation and deliverability of mail sent through other ESPs on the same subdomain.
- Enhanced Maintenance and Diagnosis: Separating subdomains by tool or mail stream simplifies maintenance, makes diagnosing deliverability issues more straightforward, and allows for clearer performance tracking.
Key considerations
- Confirm with IT: It is advisable to consult with your IT group or DNS administrator to confirm specific 'authentication records' concerns and ensure proper configuration.
- CNAME Authentication Benefit: CNAME authentication is a preferred method as it creates a unique subdomain for authorization specific to an application, potentially simplifying DNS record management.
- Diagnosing Deliverability Challenges: Sharing subdomains can significantly complicate the diagnosis of deliverability issues, as poor performance from one tool can negatively impact mail sent via another.
- Strategic Stream Separation: Beyond separating by tool, subdomains are best used to isolate different email streams, such as transactional versus marketing mail, to manage and protect their individual reputations.
Expert view
Expert from Email Geeks recommends separating subdomains by tool for easier maintenance. She also suggests CNAME authentication as a preferred method, noting that it creates a unique subdomain for authorization for that application only, which may help with managing DNS records. She advises confirming the specific type of 'authentication records' concern with the IT group.
14 Sep 2023 - Email Geeks
Expert view
Expert from Word to the Wise explains that it is generally not a best practice to use the same subdomain across multiple sending tools or ESPs. She advises against it because each ESP manages its own sending reputation for the domains it uses, and sharing a subdomain can make it difficult to diagnose deliverability issues and could allow poor performance from one ESP to negatively impact mail sent via another. It is better to use unique subdomains for each ESP.
11 Nov 2022 - Word to the Wise
What the documentation says
3 technical articles
For optimal email deliverability, particularly when utilizing multiple sending services or diverse email types, the consensus among major providers is to employ distinct subdomains. This strategic approach offers enhanced control over sender reputation, effectively isolating different email streams like marketing or transactional mail, and prevents potential deliverability issues from one source from affecting another's crucial communications.
Key findings
- Distinct Subdomains for Isolation: Major email service providers advocate using unique subdomains for different email types or sending platforms to isolate sender reputation, safeguarding deliverability across all streams.
- Greater Reputation Control: Employing a dedicated subdomain provides more direct control over your sender reputation compared to relying on an ESP's default sending settings.
- Streamlined Authentication Delegation: Authenticating a subdomain empowers the sending service to manage critical authentication protocols like DKIM signing and SPF alignment, enhancing trust with receiving servers.
- Protection for Main Domain: Utilizing subdomains helps to prevent deliverability issues associated with email sending from impacting the core reputation of your primary website domain.
- Tailored for Diverse Sending Needs: This strategy is particularly valuable when managing varied email campaigns, such as transactional messages and marketing newsletters, through multiple tools.
Key considerations
- Verification of Subdomains: Email sending platforms, such as AWS SES, support verifying multiple subdomains, enabling granular control over different sending streams.
- Isolating Mail Stream Performance: Using distinct subdomains for different email types, such as transactional, marketing, or notification emails, ensures that the performance of one stream does not compromise the deliverability of others.
- Preventing Root Domain Conflicts: Setting up subdomains specifically for email sending minimizes the risk of negative sender reputation affecting your main website domain.
- ESPs Support Subdomain Use: Leading email service providers like Mailchimp and SendGrid explicitly support and recommend authenticating subdomains for improved deliverability and reputation management.
Technical article
Documentation from Mailchimp Knowledge Base explains that authenticating a domain by setting up SPF and DKIM records helps improve deliverability. While Mailchimp can send on your behalf using their default settings, using a subdomain provides greater control over your sender reputation and is a recommended practice to avoid potential conflicts with your root domain, especially when using multiple sending services.
25 Mar 2023 - Mailchimp Knowledge Base
Technical article
Documentation from SendGrid Docs shares that domain authentication, typically using a subdomain, is crucial for email deliverability. By authenticating a subdomain, you delegate sending responsibility to SendGrid, allowing them to sign your emails with DKIM and align SPF. This practice isolates the reputation of your marketing or transactional emails from your main domain and is particularly beneficial when using different sending tools, as each can have its own dedicated subdomain for reputation management.
17 May 2024 - SendGrid Docs
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