Summary
Email subdomains are a strategic tool for enhancing deliverability, primarily by isolating sending reputations for different types of email traffic. They allow you to segment your email streams- such as transactional, promotional, and corporate communications- so that deliverability issues in one stream do not affect the others. This separation is crucial for protecting your main domain's reputation and ensuring critical messages always reach the inbox. Implementing subdomains also provides more granular control over authentication settings and simplifies management, especially when working with an Email Service Provider. It is highly recommended to implement subdomains as early as possible, ideally when setting up with a new ESP, and to use distinct subdomains for different types of email content and audience segments.
Key findings
- Reputation Isolation: Subdomains allow you to establish and maintain distinct sending reputations for different email types, such as transactional messages, promotional campaigns, or corporate communications. This prevents deliverability issues from one stream, like marketing, from negatively impacting others.
- Main Domain Protection: By segmenting email traffic, subdomains shield your main domain's reputation from the potentially lower engagement rates or higher complaint volumes often associated with bulk or marketing emails.
- Enhanced Deliverability for Critical Emails: Using subdomains ensures that essential transactional emails, such as order confirmations or password resets, maintain high deliverability even if promotional campaigns encounter issues.
- Granular Authentication and Delegation: Subdomains support more granular authentication configurations, including SPF and DKIM. Their management can often be delegated to an ESP, simplifying setup. This also facilitates a quicker move to more restrictive DMARC policies.
- ISP Categorization: Subdomains assist Internet Service Providers (ISPs) in accurately categorizing different types of email traffic, which can positively influence overall deliverability.
- Reputation Variance in Analytics: Tools like Gmail Postmaster Tools can report significantly different reputations for subdomains belonging to the same organizational domain, emphasizing their individual standing and performance.
Key considerations
- Early Implementation: It is advisable to implement subdomains as early as possible, ideally during the warmup phase with a new Email Service Provider (ESP), to establish separate reputations from the start.
- Strategic Traffic Segmentation: Utilize separate subdomains for distinct email traffic types- such as marketing, transactional, or cold outreach- and even for different audience segments like B2B versus B2C, to manage their unique sending patterns and recipient engagement.
- Coordinated Warmup: When introducing new subdomains or IP addresses, warm them up together. This combined approach efficiently establishes a healthy sending reputation for your segmented email streams.
- DMARC Policies: While DMARC policies set on your organizational domain inherently cover all subdomains, you have the flexibility to define specific, potentially more restrictive, DMARC policies for individual subdomains as needed.
- ESP's Role in Authentication and Encryption: Your ESP typically manages critical aspects like the Return-Path header and handles Transport Layer Security (TLS) for email encryption. Understand the difference between opportunistic TLS, which encrypts when possible, and mandatory TLS, which prevents transfer if encryption fails, as TLS is vital for message security.
- Flexibility and Risk Mitigation: Subdomains provide significant flexibility for managing diverse email streams. They are essential for compartmentalizing risk and safely testing new sending strategies without affecting the deliverability of your primary email communications.
- Avoiding New Domains: Generally, registering an entirely new top-level domain solely for email sending is not necessary. Subdomains offer sufficient separation and management benefits for most email strategies.
What email marketers say
16 marketer opinions
Email subdomains are a powerful strategy for enhancing deliverability by allowing senders to segment their email traffic and manage distinct sending reputations. This approach is invaluable for protecting the core domain's reputation, especially when managing diverse email streams such as promotional, transactional, and operational messages. Implementing subdomains helps ensure that critical communications maintain high deliverability even if other types of emails encounter issues. It also simplifies the management of authentication protocols and offers greater flexibility, particularly when integrating with an Email Service Provider. Strategic implementation, ideally when a new ESP relationship begins, allows for optimal reputation building and risk mitigation across all email campaigns.
Key opinions
- Reputation Segmentation: Subdomains facilitate the separation of sending reputations for different email types- such as promotional, transactional, or corporate communications. This isolation ensures that issues in one stream do not compromise the deliverability of others.
- Main Domain Shielding: By segmenting email traffic, subdomains protect your primary domain's reputation from the lower engagement rates or higher complaint volumes sometimes associated with bulk or marketing emails.
- Critical Email Assurance: The use of subdomains ensures that essential transactional emails, like order confirmations, consistently reach the inbox, even if marketing campaigns face deliverability challenges.
- Improved ISP Categorization: Internet Service Providers (ISPs) can more accurately categorize different email types when sent from distinct subdomains, which can positively influence overall deliverability and inbox placement.
- Distinct Analytics Performance: Tools such as Gmail Postmaster Tools can show significantly different reputation metrics for subdomains originating from the same primary domain, highlighting their individual sending health and performance.
- Simplified Risk Management: Subdomains allow for compartmentalized risk management, enabling senders to test new strategies or manage campaigns with higher potential for deliverability issues without jeopardizing their entire email program.
Key considerations
- Strategic Implementation Timing: Subdomains are best implemented when starting with a new Email Service Provider or during the warmup phase, allowing for the immediate establishment of distinct reputations. They are also crucial when scaling email volume or when one type of email begins to negatively affect the deliverability of others.
- Differentiation for B2B vs. B2C: Consider using separate subdomains for B2B and B2C campaigns due to their differing data, sending patterns, and reputation management challenges. Each of these would require its own warmup process.
- DMARC Policy Management: While DMARC policies on your main organizational domain will apply to all subdomains, you can set specific, potentially more restrictive, DMARC policies for individual subdomains. A new subdomain can facilitate a quicker move to more stringent DMARC enforcement.
- TLS Configuration and Importance: Ensure your ESP handles Transport Layer Security (TLS) for email encryption, which is critical for message security and favored by ISPs like Gmail. Understand the distinction between opportunistic TLS, which attempts encryption but delivers without it if not possible, and mandatory TLS, which prevents delivery if encryption fails.
- ESP Delegation and Support: Many ESPs can manage subdomain-specific configurations, including SPF, DKIM, and Return-Path headers, simplifying the setup and ongoing management of your email infrastructure.
- Avoid New Top-Level Domains: Registering an entirely new top-level domain solely for email sending is generally unnecessary, as subdomains offer ample flexibility and risk mitigation benefits.
Marketer view
Marketer from Email Geeks explains that using subdomains allows for the separation of promotional, transactional, and other correspondence types, letting them develop their own reputations. This helps ensure transactional emails are always delivered even if promotional emails encounter issues, and generally provides good organization. He confirms that the start of warmup on a new ESP is a good time to make this change.
6 May 2022 - Email Geeks
Marketer view
Marketer from Email Geeks explains that subdomains separate your bulk mailing reputation from your base domain's enterprise mail reputation. He also notes that you can delegate subdomain management, including SPF and DKIM, to your ESP. He advises setting up DMARC and mentions that a new subdomain allows for a quicker move to more restrictive DMARC policies. For B2B campaigns, he recommends moving to another separate subdomain from B2C due to different data and reputation management challenges, which would require a new warmup. He also suggests asking the ESP about mandatory versus opportunistic TLS for email encryption.
19 Aug 2024 - Email Geeks
What the experts say
3 expert opinions
Email subdomains are a strategic tool for email deliverability, primarily by enabling the isolation of sending reputation for different types of email traffic. This means that if one email stream, such as marketing campaigns, experiences deliverability challenges like complaints or spam traps, it will not negatively impact the deliverability of other critical communications, like transactional emails. Subdomains also provide more granular control over authentication settings. It is recommended to implement these as early as possible, especially for organizations with varied mail types, different internal sending departments, or when testing new email strategies, to ensure consistent and high deliverability across all streams.
Key opinions
- Reputation Isolation: A primary benefit of email subdomains is their ability to isolate sending reputation, meaning each subdomain establishes its own unique standing with mailbox providers.
- Protection for Critical Emails: Segmenting email traffic ensures that if one mail stream- like marketing campaigns- encounters deliverability issues, it won't negatively affect the crucial deliverability of other streams, such as transactional emails.
- Granular Authentication: Subdomains support more granular authentication configurations, which can sometimes be limited to a single vendor, offering more precise control over email security.
Key considerations
- Early Implementation: Experts advise implementing email subdomains as soon as possible, ideally at the outset of any new email sending setup.
- Diverse Email Streams: Subdomains are particularly beneficial for senders managing multiple distinct mail types, such as marketing, transactional, and operational emails.
- Multiple Internal Senders: When different internal departments are responsible for sending email, subdomains allow each to maintain an isolated sending reputation.
- Strategy Testing: Implementing subdomains provides a safe environment for testing new sending strategies or vendors without risking the deliverability of your main communication streams.
Expert view
Expert from Email Geeks explains that a subdomain will get its own reputation and allow for more granular authentication, limited to just one vendor. He advises implementing this change as soon as possible.
2 Jan 2024 - Email Geeks
Expert view
Expert from Spam Resource explains that email subdomains are used to isolate sending reputation, meaning if one mail stream, like marketing, encounters issues such as complaints or spam traps, it won't negatively affect the deliverability of other critical streams, like transactional emails. Implementing subdomains is particularly beneficial for senders with multiple distinct mail types, different internal departments sending email, or when testing new sending strategies, ensuring critical communications maintain strong deliverability.
30 Jul 2023 - Spam Resource
What the documentation says
3 technical articles
Email subdomains are a critical strategy for enhancing deliverability by enabling a clear separation of sending reputations across different email types. This allows businesses to specifically segment transactional and marketing communications, ensuring that any deliverability issues with promotional emails do not negatively affect the crucial delivery of system-generated messages like order confirmations. This approach is particularly beneficial for organizations with high email volumes or those managing varied communication streams, making it a foundational step in protecting the integrity and inbox placement of all email campaigns.
Key findings
- Reputation Separation: Email subdomains enable the creation of distinct sending reputations for different email types, such as transactional and marketing messages, preventing a negative impact from one affecting the other.
- Deliverability Shield: By segmenting email streams, subdomains protect against deliverability issues with one type, like marketing emails, from compromising the successful delivery of other crucial communications.
- Ensured Critical Delivery: Implementing subdomains helps guarantee that essential transactional messages maintain consistently high deliverability, even if marketing efforts encounter challenges.
Key considerations
- Strategic Segmentation Timing: Subdomains should be implemented when segmenting various email communications, especially for high-volume senders or those managing diverse email streams.
- Immediate Protection: To safeguard core communications, consider implementing subdomains immediately to establish separate sending reputations from the outset.
Technical article
Documentation from Mailgun explains that using subdomains helps isolate your sending reputation, separating transactional emails from marketing emails. This prevents issues with one type of email from affecting the deliverability of the other, and it's particularly useful for high-volume senders or those managing diverse email streams.
4 Sep 2023 - Mailgun
Technical article
Documentation from SendGrid details that subdomains are crucial for maintaining sender reputation by allowing different email types, such as transactional or marketing, to have separate sending reputations. This protection ensures that deliverability issues with one email stream do not negatively impact others, and should be implemented when segmenting various email communications.
24 Feb 2025 - SendGrid
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