Should I use a subdomain or my main domain for marketing emails?

Key findings

• Reputation isolation: Subdomains largely maintain independent sender reputations from your main domain. This separation means that if your marketing emails experience deliverability issues, like high spam complaints or blocklist listings, your main domain's reputation for transactional or corporate emails remains unaffected.
• Risk mitigation: Using a subdomain for marketing email campaigns significantly reduces the risk of your primary domain being negatively impacted by unforeseen deliverability challenges. This is crucial for businesses that rely on their main domain for critical communications.
• Volume consistency: Separating marketing emails onto a dedicated subdomain helps in maintaining consistent sending volumes, which is a factor mailbox providers consider for sender reputation. This prevents irregular spikes or drops in volume from affecting your main domain's reputation.
• Recipient experience: From the recipient's perspective, using a subdomain (e.g., newsletter@yourcompany.com) still clearly associates the email with your brand, so there is no negative impact on brand recognition or trust.
• Authentication setup: Subdomains require their own SPF and DKIM records, which allows for distinct authentication configurations without interfering with your main domain's records. This granular control over authentication is a significant advantage for deliverability.

Key considerations

• Technical setup: Implementing a subdomain involves configuring DNS records for SPF, DKIM, and DMARC separately from your main domain. While straightforward, it requires careful attention to detail to avoid misconfigurations.
• Brand recognition: Ensure the chosen subdomain clearly relates to your main brand (e.g., news.yourcompany.com) to maintain brand consistency and trust with recipients. Avoid obscure or misleading subdomains.
• Monitoring: Each subdomain you use for sending should be monitored independently for its sender reputation and deliverability performance. This allows for prompt identification and resolution of any issues specific to that sending stream.
• Email type differentiation: It's recommended to further separate different types of marketing emails (e.g., newsletters, promotional offers) onto distinct subdomains if volumes are high and engagement patterns vary significantly. This provides even greater control over reputation. More information on best practices can be found in M3AAWG's Sender Best Current Practices.

Key opinions

• Protecting the core: Marketers often prioritize protecting their primary domain, which is used for transactional emails (e.g., password resets, order confirmations), from the higher risks associated with marketing campaigns. A subdomain acts as a necessary buffer.
• Risk of blocklisting: There's a recognition that marketing emails are more prone to user complaints, spam trap hits, or being placed on an email blacklist or blocklist. Subdomains contain this risk.
• Branding vs. deliverability: While some marketers might initially prefer the main domain for strong branding, they generally understand that a deliverable email from a subdomain is far more valuable than an undelivered one from the main domain.
• Ease of management: Managing reputation on a per-subdomain basis allows for easier troubleshooting and strategy adjustments without impacting other email flows.

Key considerations

• Subdomain naming conventions: Choosing clear and intuitive subdomain names (e.g., email.yourcompany.com) is important for recipient recognition and internal organization.
• Messaging consistency: Even with a subdomain, the content, frequency, and audience engagement practices remain critical for maintaining a positive sender reputation. A subdomain isn't a silver bullet for bad sending habits. Find more tips on the basics of email subdomains.
• Cold emailing risk: For highly risky activities like cold emailing, even a subdomain might not provide sufficient isolation if the practices are poor, potentially still impacting the broader brand perception.
• Stakeholder education: Marketers often need to explain the technical benefits of subdomains to non-technical stakeholders to get buy-in for this strategy.

Key opinions

• Separation of concerns: Experts consider it best practice to separate marketing and transactional email streams onto distinct subdomains. This aligns with the principle of isolating potential reputation risks.
• MBP treatment: Mailbox providers treat different email types and sending patterns slightly differently. Separating these into subdomains allows MBPs to apply appropriate filtering and reputation scoring without penalizing critical transactional emails.
• Practical protection: A subdomain offers tangible protection to the organizational domain. While the root domain appears in the From address, the MAIL FROM (envelope sender) domain is what matters for blocklists and reputation.
• Cold emailing caveat: Experts highlight that for high-risk activities like cold emailing, even a dedicated subdomain might not be enough to prevent severe reputation damage if practices are not compliant or if the volume is too aggressive. Cousin domains may be considered in such cases.

Key considerations

• DNS records: Proper configuration of SPF, DKIM, and DMARC for each subdomain is non-negotiable for authentication and deliverability.
• Reputation building: New subdomains need to be warmed up gradually to build a positive sending history with mailbox providers. This involves starting with small volumes and slowly increasing them.
• Monitoring and response: Continuous monitoring of subdomain reputation via tools like Google Postmaster Tools or DMARC reports is essential. Quick response to any deliverability issues (e.g., blocklisting) is crucial for recovery. For more on this, check out SpamResource on subdomains and reputation.
• Vendor collaboration: When using an ESP, ensure they support dedicated subdomains and provide the necessary guidance for proper setup and authentication. This ensures technical alignment for optimal performance.

Key findings

• Reputation segmentation: Documentation consistently states that subdomains allow for segmentation of sending reputation. This means different types of email traffic (e.g., transactional, marketing) can build and maintain separate reputations, preventing issues from one stream from affecting another.
• Risk containment: A primary reason for using subdomains is to contain risk. If a marketing campaign triggers spam complaints or lands on a blocklist, only the specific subdomain's reputation is impacted, safeguarding the main domain's standing.
• Authentication flexibility: Each subdomain can have its own SPF, DKIM, and DMARC records, providing independent control over email authentication. This is crucial for maintaining proper alignment and verification, as detailed in M3AAWG's document on Sending Domains 101.
• Consistent volume patterns: Separating email types helps maintain consistent sending volumes and patterns on each subdomain, which mailbox providers favor. Irregular sending patterns on a single domain can negatively impact deliverability across all email types.

Key considerations

• Proper setup: Documentation stresses the importance of correctly setting up DNS records for each subdomain to ensure proper authentication and prevent deliverability issues. This includes careful attention to the SPF record syntax and DKIM key placement.
• Monitoring requirements: Each subdomain's deliverability and reputation must be monitored independently. Tools like Google Postmaster Tools provide insights into domain reputation. Documentation also suggests creating dedicated postmaster and abuse email addresses for each subdomain.
• Gradual warming: New subdomains should undergo a gradual warming process to build a positive reputation with mailbox providers before sending high volumes. This involves sending small, engaged batches initially and slowly scaling up.
• Alignment with policies: Ensure that the use of subdomains aligns with all relevant email authentication policies, including DMARC, to maximize deliverability and mitigate spoofing risks. This is critical for robust email security and trust.