Should transactional and marketing emails be sent from separate domains or subdomains?

Key findings

• Reputation Isolation: Separating transactional and marketing email streams, often using subdomains, effectively isolates sender reputation, reducing cross-contamination of deliverability issues.
• Engagement Impact: Transactional emails typically boast higher engagement rates, which can positively influence reputation. Conversely, marketing emails might face lower engagement or higher complaint rates, potentially damaging sender standing.
• Risk Mitigation: Isolating marketing emails to a subdomain minimizes the risk of negative impacts, such as being added to a blocklist or blacklist, from affecting critical transactional email delivery.
• Branding Consistency: Using subdomains helps retain brand consistency with the main domain, while still providing the necessary separation for deliverability.
• Industry Best Practice: The industry widely agrees that separating these email types is optimal for achieving the best possible deliverability.

Key considerations

• Setup Complexity: Implementing subdomains requires additional DNS configuration, including setting up SPF, DKIM, and DMARC records for each.
• Ongoing Monitoring: Each subdomain needs its own diligent monitoring for deliverability, blocklistings (or blacklistings), and sender reputation metrics.
• Migration Planning: A careful migration plan is crucial when moving existing email streams to new subdomains to prevent any disruption in deliverability.
• Recipient Whitelisting: Changing the From: address to a new subdomain might impact any existing customer-specific whitelisting that recipients have set up.
• Reputation Warm-up: New subdomains will require a reputation warm-up period, especially for higher sending volumes.

Key opinions

• Preference for Separation: Many marketers strongly prefer sending transactional and marketing emails from separate subdomains to protect crucial communications.
• Main Domain Protection: There is a common understanding that a dedicated subdomain for marketing helps shield the main brand domain from potential deliverability issues caused by promotional campaigns.
• Engagement Discrepancy: Marketers recognize the significant difference in engagement rates between the two types of emails, which influences their deliverability.
• Reputation Impact: They acknowledge that negative feedback, such as spam complaints on marketing emails, can severely damage the sender reputation of the main domain if not properly segmented.
• Simplified Management: Some marketers find that separating streams makes it easier to track and troubleshoot deliverability issues specific to each email type.

Key considerations

• Initial Setup Complexity: The setup and authentication of new subdomains can be a challenge for some marketing teams.
• Whitelisting Concerns: There is concern about potentially losing the benefit of recipients who have manually whitelisted the main domain's From: address when moving to a subdomain.
• Brand Perception: Some marketers express worry about a slightly diluted brand perception if customers see a subdomain for marketing rather than the primary domain.
• Increased Monitoring Burden: Managing reputation and monitoring for blocklists across multiple sending identities adds an operational layer.
• IP Warm-up Necessity: If moving to new subdomains, a careful IP warm-up strategy is essential, particularly for high-volume senders, as detailed in Mailmodo's guide on email subdomains.

Key opinions

• Reputation Segmentation: Experts agree that isolating email types to different subdomains is crucial for segmenting sender reputation.
• Transactional Protection: High-priority transactional emails must be protected from the fluctuating reputation risks often associated with marketing campaigns, as discussed in our article on separating IPs or domains for email types.
• Engagement Signals: Mailbox providers use engagement metrics, such as opens, clicks, complaints, and unsubscribes, to assess sender reputation. These signals differ significantly between email types.
• Blacklist Avoidance: Separating streams reduces the chance that a blocklist or blacklist hit on a marketing subdomain will affect the delivery of transactional or core business emails.
• Authentication Practices: Experts emphasize configuring SPF, DKIM, and DMARC correctly for each subdomain to ensure proper authentication and deliverability.

Key considerations

• Subdomain Naming: Choose descriptive and logical subdomain names, such as marketing.yourdomain.com or trans.yourdomain.com.
• Consistent Monitoring: Robust monitoring of deliverability metrics for each subdomain is essential, including bounce rates, complaint rates, and inbox placement.
• Gradual Implementation: When migrating, experts from Kickbox Blog advise a phased approach to allow for reputation building on new subdomains, as detailed in their article on sending domains and subdomains.
• DMARC Policy: Implement DMARC with a policy for all sending domains and subdomains to gain visibility into email authentication, potentially progressing to quarantine or reject policies.
• Sender Score Development: Understand that each subdomain will develop its own unique sender score or reputation with various mailbox providers.

Key findings

• Reputation Management: Documentation frequently advises segmenting email traffic by type to allow distinct reputation profiles to develop with mailbox providers.
• Risk Mitigation: Isolating marketing email, which has a higher potential for complaints or spam classification, protects the deliverability of essential transactional messages.
• Mailbox Provider Preferences: Major mailbox providers often prefer and reward senders who segment their traffic, as it simplifies their filtering processes and improves accuracy.
• Authentication Standards: Proper authentication (SPF, DKIM, DMARC) is a requirement for each sending domain or subdomain to ensure emails are trusted and delivered effectively.
• Engagement as a Signal: High engagement on transactional emails is a strong positive signal that should not be diluted by mixed sending practices, as highlighted by Mailgun's guide to email subdomains.

Key considerations

• DNS Records: Proper configuration of DNS records for each subdomain is critical for email authentication and alignment, including understanding DMARC tags and their meanings.
• Consistent Volume: Maintaining consistent sending volumes from each subdomain helps build and stabilize its reputation with receiving servers.
• Feedback Loops: Registering for feedback loops for all sending subdomains allows senders to quickly identify and address issues, such as high complaint rates.
• Monitoring Tools: Utilizing DMARC reports and other monitoring tools is essential for understanding deliverability performance across different streams.
• Policy Enforcement: DMARC policies set on a per-domain or subdomain basis can enforce authentication and instruct receivers on how to handle unauthenticated mail, helping to prevent issues like the SPF DNS timeout in Microsoft.